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  • 1.
    Akiyama, Tomoko
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Chemical and Bio-Molecular Physics.
    Björneholm, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Chemical and Bio-Molecular Physics.
    Caleman, Carl
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Chemical and Bio-Molecular Physics. Center for Free-Electron Laser Science, DESY, Notkestrasse 85, 22607 Hamburg, Germany.
    Grånäs, Oscar
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Influence of Ionization on the Dynamics of HydrocarbonsManuscript (preprint) (Other academic)
    Abstract [en]

    The structural changes of four hydrocarbons induced by ionization was investigated using molecular dynamics simulations based on density functional theory within the Born-Oppenheimer approximation. Bond lengths, bond breaking and proton rearrangement was analysed for propane, propene, propyne and propadiene at charges ranging from 0 to +3.   Similar to the case of amino acids, the back-bone of linear hydrocarbons is stabilized by reducing theeffectiv elevel of ionization through dropping protons. Subsequent iniozations, up the the level of 3+, do not break thelinear carbon chain within 250 fs, however the bond-orderis reduced, and bond-distances approach that of a single-bond

  • 2.
    Bhandary, Sumanta
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Grånäs, Oscar
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Szunyogh, Laszlo
    Sanyal, Biplab
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Nordström, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Route towards finding large magnetic anisotropy in nanocomposites: Application to a W(1-x)Re(x)/Fe multilayer2011In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 84, no 9, p. 092401-Article in journal (Refereed)
    Abstract [en]

    We suggest here a nanolaminate, 5[Fe]/2[W(x)Re(1-x)] (x = 0.6-0.8), with enhanced magnetic hardness in combination with a large saturation moment. The calculated magnetic anisotropy of this material reaches values of 5.3-7.0 MJ/m(3), depending on alloying conditions. We also propose a recipe in how to identify other novel magnetic materials, such as nanolaminates and multilayers, with large magnetic anisotropy in combination with a high saturation moment.

  • 3.
    Björkman, Torbjörn
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Materials Theory.
    Grånäs, Oscar
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Materials Theory.
    Adaptive smearing for Brillouin zone integrationManuscript (preprint) (Other (popular science, discussion, etc.))
    Abstract [en]

    We suggest a simple scheme for automatically determining the witdth parameter of smearing methods of the Brillouin zone integration in electronic structure calculation. The scheme retains one free parameter that at any time can be eliminated by choosing a denser k-space mesh until the desired accuracy is obtained. Tests are carried out in the context of Methfessel-Paxton smearing. This adaptive Gaussian smearing (AGS) is easily implemented, variational with respect to partial occupancies and free from spurious occupancies that are negative or larger than one. Its convergence properties are similar to those obtained with the modified tetrahedron method for energy resolution of ≥ 0 .1 meV.

  • 4.
    Björkman, Torbjörn
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Grånäs, Oscar
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Adaptive Smearing for Brillouin Zone Integration2011In: International Journal of Quantum Chemistry, ISSN 0020-7608, E-ISSN 1097-461X, Vol. 111, no 5, p. 1025-1030Article in journal (Refereed)
    Abstract [en]

    We suggest a simple scheme for automatically determining the width parameter of smearing methods of the Brillouin zone integration in electronic structure calculation. The scheme retains one free parameter that at any time can be eliminated by choosing a denser k-space mesh until the desired accuracy is obtained. The tests are carried out in the context of Methfessel-Paxton smearing. This adaptive Gaussian smearing (AGS) is easily implemented, variational with respect to partial occupancies and free from spurious occupancies that are negative or larger than one. Its convergence properties are similar to those obtained with the modified tetrahedron method for energy resolution of >= 0.1 meV.

  • 5.
    Björnson, Kristofer
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Wills, John Michael
    Los Alamos Natl Lab, Los Alamos, NM 87545 USA..
    Alouani, Mebarek
    Univ Strasbourg, Inst Phys & Chim Mat Strasbourg, UMR 7504 CNRS UNISTRA, Strasbourg, France..
    Grånäs, Oscar
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Thunström, Patrik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ong, Chin Shen
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Örebro Univ, Sch Sci & Technol, SE-70182 Örebro, Sweden..
    In Situ Pseudopotentials for Electronic Structure Theory2021In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 125, no 27, p. 15103-15111Article in journal (Refereed)
    Abstract [en]

    We present a general method of constructing in situ pseodopotentials from first-principles, all-electron, and full-potential electronic structure calculations of a solid. The method is applied to bcc Na, at low-temperature equilibrium volume. The essential steps of the method involve (i) calculating an all-electron Kohn-Sham eigenstate, (ii) replacing the oscillating part of the wave function (inside the muffin-tin spheres) of this state, with a smooth function, (iii) representing the smooth wave function in a Fourier series, and (iv) inverting the Kohn-Sham equation, to extract the pseudopotential that produces the state generated in steps i-iii. It is shown that an in situ pseudopotential can reproduce an all-electron full-potential eigenvalue up to the sixth significant digit. A comparison of the all-electron theory, in situ pseudopotential theory, and the standard nonlocal pseudopotential theory demonstrates good agreement, e.g., in the energy dispersion of the 3s band state of bcc Na.

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  • 6.
    Bultmark, Fredrik
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Cricchio, Francesco
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Grånäs, Oscar
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Nordström, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Multipole decomposition of LDA+U energy and its application to actinides compounds2009In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 80, no 3, p. 035121-Article in journal (Refereed)
    Abstract [en]

    A general reformulation of the exchange energy of 5f shell is applied   in the analysis of the magnetic structure of various actinides compounds in the framework of LDA + U method. The calculations are   performed in a convenient scheme with essentially only one free   parameter, the screening length. The results are analyzed in terms of  different polarization channels due to different multipoles. Generally   it is found that the spin-orbital polarization is dominating. This can   be viewed as a strong enhancement of the spin-orbit coupling in these   systems. This leads to a drastic decrease in spin polarization in   accordance with experiments. The calculations are able to correctly   differentiate magnetic and nonmagnetic Pu system. Finally, in all   magnetic systems an unusual multipolar order is observed, whose   polarization energy is often larger in magnitude than the one of spin polarization.

  • 7.
    Caleman, Carl
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy. Ctr Free Electron Laser Sci, Notkestr 85, DE-22607 Hamburg, Germany..
    Junior, Francisco Jares
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Grånäs, Oscar
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Martin, Andrew, V
    RMIT Univ, Sch Sci, Melbourne, Vic 3000, Australia..
    A Perspective on Molecular Structure and Bond-Breaking in Radiation Damage in Serial Femtosecond Crystallography2020In: Crystals, ISSN 2073-4352, Vol. 10, no 7, article id 585Article in journal (Refereed)
    Abstract [en]

    X-ray free-electron lasers (XFELs) have a unique capability for time-resolved studies of protein dynamics and conformational changes on femto- and pico-second time scales. The extreme intensity of X-ray pulses can potentially cause significant modifications to the sample structure during exposure. Successful time-resolved XFEL crystallography depends on the unambiguous interpretation of the protein dynamics of interest from the effects of radiation damage. Proteins containing relatively heavy elements, such as sulfur or metals, have a higher risk for radiation damage. In metaloenzymes, for example, the dynamics of interest usually occur at the metal centers, which are also hotspots for damage due to the higher atomic number of the elements they contain. An ongoing challenge with such local damage is to understand the residual bonding in these locally ionized systems and bond-breaking dynamics. Here, we present a perspective on radiation damage in XFEL experiments with a particular focus on the impacts for time-resolved protein crystallography. We discuss recent experimental and modelling results of bond-breaking and ion motion at disulfide bonding sites in protein crystals.

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  • 8.
    Costa, Marcio
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Grånäs, Oscar
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Bergman, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Venezuela, P.
    Instituto de Física, Universidade Federal Fluminense, Rio de Janeiro, Brasilien.
    Nordblad, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Klintenberg, Mattias
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Large magnetic anisotropy of Fe2P investigated via ab initio density functional theory calculations2012In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 86, no 8, p. 085125-Article in journal (Refereed)
    Abstract [en]

    We present an investigation of the large magnetic anisotropy of Fe2P, based on ab initio density functional theory calculations, with a full-potential linear muffin-tin orbital basis. We obtain a uniaxial magnetic anisotropy energy (MAE) of 664 mu eV/f.u., which is in decent agreement with experimental observations. Based on a band structure analysis the microscopic origin of the large magnetic anisotropy is explained. We also show that by straining the crystal structure, the MAE can be enhanced further.

  • 9.
    Cricchio, Francesco
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Bultmark, Fredrik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Grånäs, Oscar
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Nordström, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Itinerant Magnetic Multipole Moments of Rank Five as the Hidden Order in URu2Si22009In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 103, no 10, p. 107202-Article in journal (Refereed)
    Abstract [en]

    A broken symmetry ground state without any magnetic moments has been   calculated by means of the local-density approximation to density   functional theory plus a local exchange term, the so-called LDA+U   approach, for URu2Si2. The solution is analyzed in terms of a multipole   tensor expansion of the itinerant density matrix and is found to be a   nontrivial magnetic multipole. Analysis and further calculations show   that this type of multipole enters naturally in time reversal breaking   in the presence of large effective spin-orbit coupling and coexists   with magnetic moments for most magnetic actinides.

  • 10.
    Cricchio, Francesco
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Grånäs, Oscar
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Nordström, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Low spin moment due to hidden multipole order from spin-orbital ordering in LaFeAsO2010In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 81, no 14, p. 140403-Article in journal (Refereed)
    Abstract [en]

    An antiferromagnetic (AF) low-moment solution, 0.35 μB / Fe, is found in the case of LaOFeAs for an intermediately strong Coulomb interaction U of 2.75 eV. This solution is stabilized over a large moment solution due to the gain in exchange energy in the formation of large multipoles of the spin magnetization density. The multipoles are of rank four and can be understood as a type of spin-orbital ordering. Parallels can be drawn to the stabilization of the AF order in, e.g., CaCuO2.

  • 11.
    Cricchio, Francesco
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Grånäs, Oscar
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Nordström, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Multipolar and orbital ordering in ferro-pnictidesManuscript (preprint) (Other academic)
    Abstract [en]

    The stability of different solutions corresponding to various arrangement of magnetic rank-4 multipoles are evaluated for the ferro-pnictides LaOFeAs, BaFe2As2 and CaFe2As2 compounds. For LaOFeAs, the ground-state solution is identified with a combination of large w4120 and w4120 multipole tensors of the magnetization density which integrates to the correct value of experimental moment. The same procedure is applied to BaFe2As2 and CaFe2 As2 where the lowest energy solution corresponds again to a combination of w4120 and w4120 multipoles, but with a magnetic moment lower than the experimental value. However, for these compounds, our calculated moment constitutes a significant improvement over previous ab-initio calculations that largely overestimate the Fe moment. Moreover for BaFe2As2 and CaFe2As2 , in the total energy curves as function of constrained spin moment, we identify a local minima close to the experimental moment.

  • 12.
    Cricchio, Francesco
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Grånäs, Oscar
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Nordström, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Multipolar magnetic ordering in actinide dioxides from first-principles calculationsManuscript (preprint) (Other academic)
    Abstract [en]

    The LDA+U method and its multipole decomposition are applied to investigate the ground state of the actinide insulators dioxides UO2 , NpO2 and PuO2 . In case of UO2 , an antifer- romagnetic 3-k type ordering of U moments is identified as one of the lowest energy solutions, in agreement with experiments and recent calculations. For NpO2 , a magnetic multipolar 3-k ordering of triakontadipoles, with a zero net magnetic moment on Np atoms, is found to be one of the most stable solutions. This is in agreement with recent investigations that predict the triakontadipoles to be the hidden order parameter in NpO2 . Also in case of the non-magnetic insulator PuO2 , the ground-state is predicted to be described by a multipolar 1-k ordering of triakontadipoles associated with a magnetization density that integrates to zero on Pu sites.

  • 13.
    Cricchio, Francesco
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Grånäs, Oscar
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Nordström, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Polarization of an open shell in the presence of spin-orbit coupling2011In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 94, no 5, p. 57009-Article in journal (Refereed)
    Abstract [en]

    There exist many f transition metal-based materials, with large orbital degeneracy and relatively strong spin-orbit coupling, that exhibits some multipolar order. We perform first-principles calculations on these systems within DFT method plus on-site Coulomb correction and we discuss the results in terms of polarization of the density occupation matrix. The fact that higher multipole polarizations play a larger role than the spin polarization indicates a breakdown of Hund's rules and we suggest a new complementary set of rules -Katt's rules, valid in case of large spin-orbit coupling interaction.

  • 14.
    Cricchio, Francesco
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Grånäs, Oscar
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Nordström, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    The role of triakontadipoles in uranium-based magnetic superconductor materialsManuscript (preprint) (Other academic)
    Abstract [en]

    We investigate the ground state of the heavy-fermion actinide compounds UPd2Al3 , UNi2Al3 and UPt3 by means of electronic structure calculations including on-site correlation. The results are analyzed through multipole decomposition. In case of UPd2Al3 and UNi2Al3 we stabilize a solution with an antiferromagnetic arrangement of triakontadipoles with ordering vectors, respectively, q = (0, 0, 1/2 ) and q = ( 1/2 , 0, 1/2 ), whose total magnetic moment agrees with the experimental value. In case of UPt3 we identify a solution with a triakontadipole order whose symmetry is not compatible with the presence of a magnetic moment, in accordance with experiments that detect a very small value of the moment. The Fermi surfaces of the multipole dominated solutions have many common features with those obtained by conventional density functional methods. Finally, for URu2Si2 we are able to stabilize a new solution characterized by a q = (0, 0, 1/2 ) ordering of triakontadipoles and a symmetry that forbids a magnetic moment on uranium site. The Fermi surface of this solution is surprisingly similar to the one of the magnetic AF 1-q case in agreement with recent measurements.

  • 15.
    Dawod, Ibrahim
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Chemical and Bio-Molecular Physics. European XFEL, Holzkoppel 4, DE-22869 Schenefeld, Germany.
    Patra Kumar, Kajwal
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Chemical and Bio-Molecular Physics.
    Cardoch, Sebastian
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Chemical and Bio-Molecular Physics.
    Jönsson, H. Olof
    Department of Applied physics, KTH Royal Institute of Technology, SE-106 91, Stockholm, Sweden.
    Sellberg, Jonas A.
    Department of Applied physics, KTH Royal Institute of Technology, SE-106 91, Stockholm, Sweden.
    Martin, Andrew V.
    School of Science, RMIT University, Melbourne, Victoria 3000, Australia.
    Binns, Jack
    School of Science, RMIT University, Melbourne, Victoria 3000, Australia.
    Grånäs, Oscar
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Mancuso, Adrian P.
    European XFEL, Holzkoppel 4, DE-22869 Schenefeld, Germany. Department of Chemistry and Physics, La Trobe Institute for Molecular Science, La Trobe University, Melbourne, Victoria 3086, Australia. Diamond Light Source, Harwell Science and Innovation Campus, Didcot OX11 0DE, UK .
    Caleman, Carl
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Chemical and Bio-Molecular Physics. Center for Free-Electron Laser Science, Deutsches Elektronen-Synchrotron, Notkestraße 85 DE-22607 Hamburg, Germany.
    Timneanu, Nicusor
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Chemical and Bio-Molecular Physics.
    Anisotropic melting of ice induced by ultrafast non-thermal heatingManuscript (preprint) (Other academic)
    Abstract [en]

    Water and ice are routinely studied with X-rays to reveal their diverse structures and anomalous properties. We employ a hybrid collisional-radiative/molecular dynamics method to explore how femtosecond X-ray pulses interact with hexagonal ice. We find that ice makes a phase transition into a crystalline plasma where its initial structure is maintained up to tens of femtoseconds. The ultrafast melting process occurs anisotropically, where different geometric configurations of the structure melt on different time scales. The transient state and anisotropic melting of crystals can be captured by X-ray diffraction, which impacts any study of crystalline structures probed by femtosecond X-ray lasers.

  • 16.
    di Marco, Igor
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Thunström, P
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Grånäs, Oscar
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Pourovskii, L
    Centre de Physique Théorique (CPHT) École Polytechnique.
    Katsnelson, M I
    Inst. for Molecules and Materials, Radboud University of Nijmegen.
    Nordström, L
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Eriksson, O
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    An LDA+DMFT study of the orbital magnetism and total energy properties of the late transition metals: conserving and non-conserving approximationsManuscript (preprint) (Other academic)
  • 17.
    Droulias, S. A.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Grånäs, Oscar
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Hartmann, Ola
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Komander, Kristina
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
    Hjörvarsson, Björgvin
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Wolff, Max
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Pálsson, Gunnar K.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Influence of deuterium-induced volume changes on optical transmission in Fe/V (001) and Cr/V (001) superlattices2022In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 105, no 19, article id 195438Article in journal (Refereed)
    Abstract [en]

    The deuterium-induced changes of the optical transmission in Fe/V (001) and Cr/V (001) superlattices are found experimentally to be dominated by the volume changes of the vanadium layers and thus indirectly linked to concentration. The deuterium-induced expansion is 67% larger in Cr/V 2/14 monolayers (ML) as compared to Fe/V 2/14 ML. This large difference can be explained by a difference in the site of deuterium from tetrahedral in Fe/V to octahedral in Cr/V. First-principles calculations based on this assumption give quantitative agreement with both the measured optical transmission and the deuterium-induced expansion coefficient. Placing hydrogen in the middle of the vanadium layers results in total energies at 0 K that favor tetrahedral occupancy at low concentrations, although the energy difference is of the order of the thermal energy available in the experiments. Hence small changes in strain, defect concentration, and/or vibrational spectrum of the superlattices may tip the balance to octahedral occupancy at low concentrations. Given this link to concentration and the linear scaling, optical transmission can, therefore, be used in a straightforward way to obtain pressure-composition isotherms also in thin metal films that do not undergo metal-insulator transitions upon hydrogenation.

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  • 18.
    Droulias, Sotirios A.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Grånäs, Oscar
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Hartmann, Ola
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Komander, Kristina
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Wolff, Max
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Hjörvarsson, Björgvin
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Pálsson, Gunnar K.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Tailoring thermodynamic properties of metal hydrides with interfacesManuscript (preprint) (Other academic)
    Abstract [en]

    We report profound changes in the enthalpy of solution and critical temperature of nano-sizedmetal hydrides in proximity to dierent non-absorbing metals. We use Cr/V and Fe/V (001) superlatticesas model systems to map out these eects since the superlattices can be made singlecrystalline,have identical strain states and are fully reversible. The thermodynamic propertiesare determined using isothermal pressure and optical transmission measurements. We determinethe mechanism underlying the changes in the thermodynamic properties as well as the ecacyof optical transmission by utilizing simultaneous neutron reectometry and optical transmissionmeasurements, combined with rst principle calculations. The underlying mechanism, which issupported by quantitative agreement between theory and experiment is found to be rooted in aradically dierent volume expansion in the two systems. The commonly used optical transmissionmethod is found to be linear with concentration in both types of superlattices and is attributed tochanges in electron density, rather than a direct inuence from a redistribution of electronic states.The conclusions are generalized to other metal hydride systems and can open up for exploration ofproximity induced eects in metal hydrides.

  • 19.
    Droulias, Sotirios A.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Grånäs, Oscar
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Hartmann, Ola
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Komander, Kristina
    Wolff, Max
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Hjörvarsson, Björgvin
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Pálsson, Gunnar K.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Using interfaces to influence thermodynamic properties of metal hydridesManuscript (preprint) (Other academic)
    Abstract [en]

    We report profound proximity effects on the enthalpy of solution and critical temperature ofnano-sized vanadium hydrides. We use single crystalline Cr/V and Fe/V (001) superlattices forthese studies, in which the V layers are under close to identical strain. The thermodynamic propertiesare determined using isothermal pressure and optical transmission measurements, utilisingthe fully reversibel hydrogen uptake and release.The underlying mechanism is argued to be rootedin a radically different volume expansion in the two systems, arising from different site occupancyof hydrogen in Fe/V(001) and Cr/V(001). The optical transmission is found to be linear withconcentration in both types of superlattices, while exhibiting different slopes. The differences areattributed to changes in electron density arising from the volume expansion, rather than a directinfluence from a redistribution of electronic states.

  • 20.
    Elhanoty, Mohamed F.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Örebro Univ, Sch Sci & Technol, SE-70182 Örebro, Sweden..
    Knut, Ronny
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Condensed Matter Physics of Energy Materials.
    Karis, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Condensed Matter Physics of Energy Materials.
    Grånäs, Oscar
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Different fingerprints for the OISTR mechanism in the magnetic alloys experiments2022In: ADVANCES IN ULTRAFAST CONDENSED PHASE PHYSICS III / [ed] Haacke, S Yakovlev, V, SPIE-Intl Soc Optical Eng SPIE - The International Society for Optics and Photonics, 2022, Vol. 12132, article id 121320BConference paper (Refereed)
    Abstract [en]

    The interplay between various degrees of freedom in laser induced ultrafast magnetization dynamics (LIUMD) of magnetic alloys is intricate due to the competition between different mechanisms and processes. In this work, we resolve the element specific magnetization dynamics of FePd alloy and further elucidate the dependency of the OISTR mechanism on the laser pulse parameters using ultrashort, short and relatively longer pulse duration with weak and strong fluence. Remarkably, our results illustrate potential discrepancies in experiments measuring the optical inter site spin transfer (OISTR) effect in magnetic alloys.

  • 21.
    Elhanoty, Mohamed F.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Örebro Univ, Sch Sci & Technol, SE-70182 Örebro, Sweden..
    Knut, Ronny
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Karis, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Grånäs, Oscar
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Element-selective ultrafast magnetization dynamics of hybrid Stoner-Heisenberg magnets2022In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 105, no 10, article id L100401Article in journal (Refereed)
    Abstract [en]

    Stoner and Heisenberg excitations in magnetic materials are inherently different. The first involves an effective reduction of the exchange splitting, whereas the second comprises excitation of spin waves. In this work, we test the impact of these two excitations in the hybrid Stoner-Heisenberg system of FePd. We present a microscopic picture of ultrafast demagnetization dynamics in this alloy, which represents both components of strong local exchange splitting in Fe and induced polarization in Pd. We identify the spin-orbit coupling (SOC) and the optical intersite spin transfer (OISTR) as the two dominant factors for demagnetization at ultrashort timescales. Remarkably, the drastic difference in the origin of the magnetic moment of the Fe and Pd species is not deciding the initial magnetization dynamics in this alloy. By tuning the external laser pulse, the extrinsic OISTR can be manipulated for site-selective demagnetization on femtosecond timescales providing the fastest way for optical and selective control of the magnetization dynamics in alloys. Saliently, our results signify why various experiments demonstrating OISTR might obtain conflicting results.

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    FULLTEXT01
  • 22.
    Eliah Dawod, Ibrahim
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Chemical and Bio-Molecular Physics. European XFEL, Holzkoppel 4, DE-22869 Schenefeld, Germany.
    Timneanu, Nicusor
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Chemical and Bio-Molecular Physics.
    Mancuso, Adrian P.
    European XFEL, Holzkoppel 4, DE-22869 Schenefeld, Germany.;La Trobe Univ, La Trobe Inst Mol Sci, Dept Chem & Phys, Melbourne, Vic 3086, Australia..
    Caleman, Carl
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Chemical and Bio-Molecular Physics. DESY, Ctr Free Electron Laser Sci, Notkestr 85, DE-22607 Hamburg, Germany.
    Grånäs, Oscar
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Imaging of femtosecond bond breaking and charge dynamics in ultracharged peptides2022In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 24, no 3, p. 1532-1543Article in journal (Refereed)
    Abstract [en]

    X-ray free-electrons lasers have revolutionized the method of imaging biological macromolecules such as proteins, viruses and cells by opening the door to structural determination of both single particles and crystals at room temperature. By utilizing high intensity X-ray pulses on femtosecond timescales, the effects of radiation damage can be reduced. Achieving high resolution structures will likely require knowledge of how radiation damage affects the structure on an atomic scale, since the experimentally obtained electron densities will be reconstructed in the presence of radiation damage. Detailed understanding of the expected damage scenarios provides further information, in addition to guiding possible corrections that may need to be made to obtain a damage free reconstruction. In this work, we have quantified the effects of ionizing photon-matter interactions using first principles molecular dynamics. We utilize density functional theory to calculate bond breaking and charge dynamics in three ultracharged molecules and two different structural conformations that are important to the structural integrity of biological macromolecules, comparing to our previous studies on amino acids. The effects of the ultracharged states and subsequent bond breaking in real space are studied in reciprocal space using coherent diffractive imaging of an ensemble of aligned biomolecules in the gas phase.

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    fulltext
  • 23. Esteban-Puyuelo, Raquel
    et al.
    Sanyal, Biplab
    Grånäs, Oscar
    Graphene nanoflakes as a testbed for electronic structure analysis through high harmonic generationManuscript (preprint) (Other academic)
  • 24.
    Esteban-Puyuelo, Raquel
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Sonkar, Rajat Kumar
    Savitribai Phule Pune Univ, Ctr Modeling & Simulat, Pune 411007, Maharashtra, India..
    Pujari, Bhalchandra
    Savitribai Phule Pune Univ, Ctr Modeling & Simulat, Pune 411007, Maharashtra, India..
    Grånäs, Oscar
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Sanyal, Biplab
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Tailoring the opto-electronic response of graphene nanoflakes by size and shape optimization2020In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 22, no 15, p. 8212-8218Article in journal (Refereed)
    Abstract [en]

    The long spin-diffusion length, spin-lifetime and excellent optical absorption coefficient of graphene provide an excellent platform for building opto-electronic devices and spin-based logic in a nanometer regime. In this study, by using density functional theory and its time-dependent version, we provide a detailed analysis of how the size and shape of graphene nanoflakes can be used to alter their magnetic structures and optical properties. As the edges of zigzag graphene nanoribbons are known to align anti-ferromagnetically and armchair nanoribbons are typically non-magnetic, a combination of both in a nanoflake geometry can be used to optimize the ground-state magnetic structure and tailor the exchange coupling decisive for ferro- or anti-ferromagnetic edge magnetism, thereby offering the possibility to optimize the external fields needed to switch magnetic ordering. Most importantly, we show that the magnetic state alters the optical response of the flake leading to the possibility of opto-spintronic applications.

  • 25.
    Galchenkova, Marina
    et al.
    Center for Free-Electron Laser Science, Deutsches Elektronen-Synchrotron, Notkestraße 85, DE-22607 Hamburg, Germany.
    Dawod, Ibrahim
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Chemical and Bio-Molecular Physics. European XFEL, Holzkoppel 4, DE-22869 Schenefeld, Germany.
    Sprenger, Janina
    Center for Free-Electron Laser Science, Deutsches Elektronen-Synchrotron, Notkestraße 85, DE-22607 Hamburg, Germany.
    Oberthur, Dominik
    Center for Free-Electron Laser Science, Deutsches Elektronen-Synchrotron, Notkestraße 85, DE-22607 Hamburg, Germany.
    Cardoch, Sebastian
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Chemical and Bio-Molecular Physics.
    De Santis, Emiliano
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Biochemistry.
    Grånäs, Oscar
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Timneanu, Nicusor
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Chemical and Bio-Molecular Physics.
    Chapman, Henry N.
    Center for Free-Electron Laser Science, Deutsches Elektronen-Synchrotron, Notkestraße 85, DE-22607 Hamburg, Germany. Centre for Ultrafast Imaging, Universität Hamburg, 22761 Hamburg, Germany. Department of Physics, Universität Hamburg, 22761 Hamburg, Germany .
    Caleman, Carl
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Chemical and Bio-Molecular Physics. Center for Free-Electron Laser Science, Deutsches Elektronen-Synchrotron, Notkestraße 85, DE-22607 Hamburg, Germany.
    Yefanov, Oleksandr
    Center for Free-Electron Laser Science, Deutsches Elektronen-Synchrotron, Notkestraße 85, DE-22607 Hamburg, Germany.
    Radiation damage in a hemoglobin crystal studied with an X-ray free-electron laserManuscript (preprint) (Other academic)
    Abstract [en]

    Radiation damage is a topic since the dawn of X-ray crystallography, and has gained new importance in the era of X-ray free-electron lasers (XFELs), due to their unprecedented brilliance and pulse duration. One of the driving questions has been how short the XFEL pulse has to be for the structural information to be ”damage free”. Here we compare data from Serial Femtosecond Crystallography (SFX) experiments conducted with a 3 fs and a 10 fs X-ray pulse. We conclude that even if the estimated displacement of atoms in the sample is an order of magnitude larger in the case of the 10 fs experiment, the displacement is still too small to affect the experimental data at a resolution relevant for structural determination.

  • 26.
    Ganguly, Shreemoyee
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Granas, Oscar
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Nordstrom, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Nontrivial order parameter in Sr2IrO42015In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 91, no 2, p. 020404-Article in journal (Refereed)
    Abstract [en]

    A thorough analysis of the ground state of the relativistic magnetic insulator Sr2IrO4 is performed. The results are in accordance with the small antiferromagnetic moment and gapped state found in experiment. The solution, obtained using the DFT+SO+U methodology, is thoroughly analyzed in terms of Landau theory. We find that the ordered magnetic moment only forms a secondary order parameter while the primary order parameter is a higher order magnetic multipole of rank five. It is further observed that the electronic structure in the presence of this order parameter is related to the earlier proposed j(eff) = 1/2 model, but in contrast to that model, the present picture can exactly explain the small magnitude of the ordered magnetic moments.

  • 27.
    Gopakumar, Geethanjali
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Chemical and Bio-Molecular Physics.
    Svensson, Pamela
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Chemical and Bio-Molecular Physics.
    Grånäs, Oscar
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Brena, Barbara
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Physics. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Schwob, Lucas
    Deutsch Elektronen Synchrotron DESY, DE-22607 Hamburg, Germany..
    Unger, Isaak
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Chemical and Bio-Molecular Physics.
    Saak, Clara-Magdalena
    Univ Vienna, Dept Phys Chem, A-1090 Vienna, Austria..
    Timm, Martin
    Helmholtz Zentrum Berlin Mat & Energie, Abt Hochempfindl Rontgenspektroskopie, DE-12489 Berlin, Germany.;Tech Univ Berlin, Inst Opt & Atomare Phys, DE-10623 Berlin, Germany..
    Buelow, Christine
    Helmholtz Zentrum Berlin Mat & Energie, Abt Hochempfindl Rontgenspektroskopie, DE-12489 Berlin, Germany.;Albert Ludwigs Univ Freiburg, Phys Inst, DE-79104 Freiburg, Germany..
    Kubin, Markus
    Helmholtz Zentrum Berlin Mat & Energie, Abt Hochempfindl Rontgenspektroskopie, DE-12489 Berlin, Germany..
    Zamudio-Bayer, Vicente
    Helmholtz Zentrum Berlin Mat & Energie, Abt Hochempfindl Rontgenspektroskopie, DE-12489 Berlin, Germany..
    Lau, J. Tobias
    Helmholtz Zentrum Berlin Mat & Energie, Abt Hochempfindl Rontgenspektroskopie, DE-12489 Berlin, Germany.;Albert Ludwigs Univ Freiburg, Phys Inst, DE-79104 Freiburg, Germany..
    von Issendorff, Bernd
    Albert Ludwigs Univ Freiburg, Phys Inst, DE-79104 Freiburg, Germany..
    Abid, Abdul Rahman
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy. Univ Oulu, Fac Sci, Nano & Mol Syst Res Unit, Oulu 90570, Finland..
    Lindblad, Andreas
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Danielsson, Emma
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Koerfer, Ebba
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Caleman, Carl
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy. Deutsch Elektronen Synchrotron DESY, Ctr Free Electron Laser Sci, DE-22607 Hamburg, Germany..
    Björneholm, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Lindblad, Rebecka
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy. Helmholtz Zentrum Berlin Mat & Energie, Abt Hochempfindl Rontgenspektroskopie, DE-12489 Berlin, Germany.;Lund Univ, Dept Phys, SE-22100 Lund, Sweden.;Uppsala Univ, Dept Chem, Angstrom Lab, SE-75121 Uppsala, Sweden..
    X-ray Induced Fragmentation of Protonated Cystine2022In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 126, no 9, p. 1496-1503Article in journal (Refereed)
    Abstract [en]

    We demonstrate site-specific X-ray induced fragmentation across the sulfur L-edge of protonated cystine, the dimer of the amino acid cysteine. Ion yield NEXAFS were performed in the gas phase using electrospray ionization (ESI) in combination with an ion trap. The interpretation of the sulfur Ledge NEXAFS spectrum is supported by Restricted Open-Shell Configuration Interaction (ROCIS) calculations. The fragmentation pathway of triply charged cystine ions was modeled by Molecular Dynamics (MD) simulations. We have deduced a possible pathway of fragmentation upon excitation and ionization of S 2p electrons. The disulfide bridge breaks for resonant excitation at lower photon energies but remains intact upon higher energy resonant excitation and upon ionization of S 2p. The larger fragments initially formed subsequently break into smaller fragments.

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    FULLTEXT01
  • 28.
    Gopakumar, Geethanjali
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Chemical and Bio-Molecular Physics.
    Svensson, Pamela H.W.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Chemical and Bio-Molecular Physics.
    Grånäs, Oscar
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Brena, Barbara
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Schwob, L
    Deutsches Elektronen-Synchrotron DESY, Notkestrasse 85, DE-22607 Hamburg, Germany.
    Unger, Isaak
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Chemical and Bio-Molecular Physics.
    Saak, Clara-Magdalena
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Chemical and Bio-Molecular Physics.
    Timm, M
    Abteilung für Hochempfindliche Röntgenspektroskopie, Helmholtz-Zentrum Berlin für Materialien und Energie, Albert-Einstein-Strasse 15, DE-12489 Berlin, Germany; nstitut für Optik und Atomare Physik, Technische Universität Berlin, Hardenbergstrasse 36, DE-10623 Berlin, Germany.
    Bülow, C
    Abteilung für Hochempfindliche Röntgenspektroskopie, Helmholtz-Zentrum Berlin für Materialien und Energie, Albert-Einstein-Strasse 15, DE-12489 Berlin, Germany; Physikalisches Institut, Albert-Ludwigs-Universität Freiburg, Hermann-Herder-Strasse 3, DE-79104 Freiburg, Germany.
    Kubin, M
    Abteilung für Hochempfindliche Röntgenspektroskopie, Helmholtz-Zentrum Berlin für Materialien und Energie, Albert-Einstein-Strasse 15, DE-12489 Berlin, Germany.
    Zamudio-Bayer, V
    Abteilung für Hochempfindliche Röntgenspektroskopie, Helmholtz-Zentrum Berlin für Materialien und Energie, Albert-Einstein-Strasse 15, DE-12489 Berlin, Germany.
    Lau, J-T
    Abteilung für Hochempfindliche Röntgenspektroskopie, Helmholtz-Zentrum Berlin für Materialien und Energie, Albert-Einstein-Strasse 15, DE-12489 Berlin, Germany; Physikalisches Institut, Albert-Ludwigs-Universität Freiburg, Hermann-Herder-Strasse 3, DE-79104 Freiburg, Germany.
    von Issendorff, B
    Physikalisches Institut, Albert-Ludwigs-Universität Freiburg, Hermann-Herder-Strasse 3, DE-79104 Freiburg, Germany.
    Abid, Abdul Rahman
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Chemical and Bio-Molecular Physics. Nano and Molecular Systems Research Unit, Faculty of Science, University of Oulu, P. O. Box 3000, Finland.
    Lindblad, Andreas
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Danielsson, E
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Koerfer, E
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Caleman, Carl
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Chemical and Bio-Molecular Physics. Center for Free-Electron Laser Science, Deutsches Elektronen-Synchrotron DESY, Notkestrasse 85, DE-22607 Hamburg, Germany.
    Björneholm, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Chemical and Bio-Molecular Physics.
    Lindblad, Rebecka
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry. Department of Physics, Lund University, Box 118, SE-22100 Lund, Sweden; Abteilung für Hochempfindliche Röntgenspektroskopie, Helmholtz-Zentrum Berlin für Materialien und Energie, Albert-Einstein-Strasse 15, DE-12489 Berlin, Germany.
    X-ray Induced Fragmentation of Protonated CystineManuscript (preprint) (Other academic)
    Abstract [en]

    Protein structure determination using high-intensity X-ray sources induces damage in the protein. Disulfide bridges, formed between two cysteine amino acid residues stabilize the protein structure. Owing to the higher absorption cross-section of sulfur for X-ray photons, and a large number of electrons released from sulfur atoms, these disulfide bridges are hot spots for a higher level of noise in structural studies. But it is yet to be understood how exactly the damage occurs through the interaction of the disulfide bridges with photons. Here we study the fragmentation of protonated cystine in the gas phase, which is the dimer of cysteine, by irradiation with X-rays across the sulfur L-edge using an electrospray ionization source (ESI) in combination with an ion trap. This is complemented with the calculation of the sulfur NEXAFS spectrum on the level of Restricted Open-Shell Configuration Interaction (ROCIS) and Density Functional Theory (DFT) calculations for molecular orbital visualization as well as Molecular Dynamics (MD) simulations for the fragmentation of triply charged cystine ions. We have deduced a possible pathway of fragmentation upon excitation and ionization of S 2p electrons by combining the experiments and simulations. The disulfide bridge breaks for resonant excitation at lower energies but remains intact upon higher energy resonant excitation and upon ionization of S 2p. The larger fragments formed subsequently break into smaller fragments. 

  • 29.
    Grånäs, Oscar
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Theoretical Studies of Magnetism and Electron Correlation in Solids2012Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This work presents new development and applications of ab-initio simulation tools for material science. Focus lies on materials with strong electronic correlation and strong spin-orbit coupling. Improvements on methods for solving the impurity problem in LDA+DMFT is presented, as well as a reliant method for charge self-consistency in a LMTO based electronic structure code. A new adaptive scheme for Brillouin zone integration is developed, where we show a strong reduction of numerical noise compared to standard techniques. A reformulation of the standard LDA+U method aiming to reduce the number of free parameters is introduced. Fast and realistic reduction of the number of free parameters provides the possibility of high throughput calculations and enabled us to study a large number of compounds. An analysis method for polarization in terms of coupled multipoles, and their corresponding energy contributions is developed and applied. This led to the formulation of Katt's rules, a set of rules complementary to Hund's rules. Katt's rules applies for occupying the orbitals of an electronic shell with strong spin-orbit coupling. The analysis is also used to investigate the unconventional Uranium based superconductors URu2Si2, UPt3, UPd2Al3 and UNi2Al3, as well as the high temperature superconductor LaOFeAs. We also investigate the non-magnetic delta-phase of Plutonium, providing insight to the electronic structure and the branching ratios of 4d to 5f transitions seen in photo emission spectra.The influence of surface reconstruction on the magneto crystalline anisotropy is investigated in multilayer Fe/ZnSe, showing that Fe deposited on an unreconstructed interface strongly reduces the uniaxial component of the MAE. We provide a detailed understanding of the magnetic properties of Fe2P, opening possible routes for enhancing the MAE in this system. A general route to strong MAE in nano-laminates is presented, we apply this to propose a candidate with extremely strong anisotropy energy density, 5Fe/2W1-xReX for x=[0.6-0.8].

    List of papers
    1. An LDA+DMFT study of the orbital magnetism and total energy properties of the late transition metals: conserving and non-conserving approximations
    Open this publication in new window or tab >>An LDA+DMFT study of the orbital magnetism and total energy properties of the late transition metals: conserving and non-conserving approximations
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    (English)Manuscript (preprint) (Other academic)
    National Category
    Condensed Matter Physics
    Research subject
    Physics with spec. in Atomic, Molecular and Condensed Matter Physics
    Identifiers
    urn:nbn:se:uu:diva-172345 (URN)
    Available from: 2012-04-05 Created: 2012-04-05 Last updated: 2012-08-01
    2. Charge self-consistent dynamical mean-field theory based on the full-potential linear muffin-tin orbital method: Methodology and applications
    Open this publication in new window or tab >>Charge self-consistent dynamical mean-field theory based on the full-potential linear muffin-tin orbital method: Methodology and applications
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    2012 (English)In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 55, p. 295-302Article in journal (Refereed) Published
    Abstract [en]

    Full charge self-consistence (CSC) over the electron density has been implemented into the local density approximation plus dynamical mean-field theory (LDA + DMFT) scheme based on a full-potential linear muffin-tin orbital method (FP-LMTO). Computational details on the construction of the electron density from the density matrix are provided. The method is tested on the prototypical charge-transfer insulator NiO using a simple static Hartree-Fock approximation as impurity solver. The spectral and ground state properties of bcc Fe are then addressed, by means of the spin-polarized T-matrix fluctuation exchange solver (SPTF). Finally the permanent magnet SmCo5 is studied using multiple impurity solvers, SPTF and Hubbard I, as the strength of the local Coulomb interaction on the Sm and Co sites are drastically different. The developed CSC-DMFT method is shown to in general improve on materials properties like magnetic moments, electronic structure and the materials density.

    Keywords
    Dynamical mean-field theory, Correlated materials, NiO, Fe, SmCo5
    National Category
    Physical Sciences
    Identifiers
    urn:nbn:se:uu:diva-171397 (URN)10.1016/j.commatsci.2011.11.032 (DOI)000300728600039 ()
    Available from: 2012-03-20 Created: 2012-03-19 Last updated: 2017-12-07Bibliographically approved
    3. Adaptive Smearing for Brillouin Zone Integration
    Open this publication in new window or tab >>Adaptive Smearing for Brillouin Zone Integration
    2011 (English)In: International Journal of Quantum Chemistry, ISSN 0020-7608, E-ISSN 1097-461X, Vol. 111, no 5, p. 1025-1030Article in journal (Refereed) Published
    Abstract [en]

    We suggest a simple scheme for automatically determining the width parameter of smearing methods of the Brillouin zone integration in electronic structure calculation. The scheme retains one free parameter that at any time can be eliminated by choosing a denser k-space mesh until the desired accuracy is obtained. The tests are carried out in the context of Methfessel-Paxton smearing. This adaptive Gaussian smearing (AGS) is easily implemented, variational with respect to partial occupancies and free from spurious occupancies that are negative or larger than one. Its convergence properties are similar to those obtained with the modified tetrahedron method for energy resolution of >= 0.1 meV.

    Keywords
    Brillouin zone integration, band structure methods, Gaussian smearing, magnetocrystalline anisotropy energy
    National Category
    Physical Sciences
    Identifiers
    urn:nbn:se:uu:diva-148949 (URN)10.1002/qua.22476 (DOI)000287163800012 ()
    Available from: 2011-03-15 Created: 2011-03-14 Last updated: 2017-12-11Bibliographically approved
    4. Multipole decomposition of LDA+U energy and its application to actinides compounds
    Open this publication in new window or tab >>Multipole decomposition of LDA+U energy and its application to actinides compounds
    2009 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 80, no 3, p. 035121-Article in journal (Refereed) Published
    Abstract [en]

    A general reformulation of the exchange energy of 5f shell is applied   in the analysis of the magnetic structure of various actinides compounds in the framework of LDA + U method. The calculations are   performed in a convenient scheme with essentially only one free   parameter, the screening length. The results are analyzed in terms of  different polarization channels due to different multipoles. Generally   it is found that the spin-orbital polarization is dominating. This can   be viewed as a strong enhancement of the spin-orbit coupling in these   systems. This leads to a drastic decrease in spin polarization in   accordance with experiments. The calculations are able to correctly   differentiate magnetic and nonmagnetic Pu system. Finally, in all   magnetic systems an unusual multipolar order is observed, whose   polarization energy is often larger in magnitude than the one of spin polarization.

    National Category
    Physical Sciences
    Identifiers
    urn:nbn:se:uu:diva-98059 (URN)10.1103/PhysRevB.80.035121 (DOI)000268617800055 ()
    Available from: 2009-02-12 Created: 2009-02-12 Last updated: 2017-12-13Bibliographically approved
    5. Analysis of dynamical exchange and correlation in terms of coupled multipoles
    Open this publication in new window or tab >>Analysis of dynamical exchange and correlation in terms of coupled multipoles
    (English)Manuscript (Other academic)
    National Category
    Physical Sciences
    Identifiers
    urn:nbn:se:uu:diva-98062 (URN)
    Available from: 2009-02-12 Created: 2009-02-12 Last updated: 2012-08-01Bibliographically approved
    6. Polarization of an open shell in the presence of spin-orbit coupling
    Open this publication in new window or tab >>Polarization of an open shell in the presence of spin-orbit coupling
    2011 (English)In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 94, no 5, p. 57009-Article in journal (Refereed) Published
    Abstract [en]

    There exist many f transition metal-based materials, with large orbital degeneracy and relatively strong spin-orbit coupling, that exhibits some multipolar order. We perform first-principles calculations on these systems within DFT method plus on-site Coulomb correction and we discuss the results in terms of polarization of the density occupation matrix. The fact that higher multipole polarizations play a larger role than the spin polarization indicates a breakdown of Hund's rules and we suggest a new complementary set of rules -Katt's rules, valid in case of large spin-orbit coupling interaction.

    Keywords
    Spin-orbit interaction, actinides, Hund's rules, correlated electrons, electronic structure calculations
    National Category
    Condensed Matter Physics
    Research subject
    Physics with spec. in Atomic, Molecular and Condensed Matter Physics
    Identifiers
    urn:nbn:se:uu:diva-132067 (URN)10.1209/0295-5075/94/57009 (DOI)000291033900033 ()
    Available from: 2010-10-13 Created: 2010-10-13 Last updated: 2022-01-28Bibliographically approved
    7. Multipolar magnetic ordering in actinide dioxides from first-principles calculations
    Open this publication in new window or tab >>Multipolar magnetic ordering in actinide dioxides from first-principles calculations
    (English)Manuscript (preprint) (Other academic)
    Abstract [en]

    The LDA+U method and its multipole decomposition are applied to investigate the ground state of the actinide insulators dioxides UO2 , NpO2 and PuO2 . In case of UO2 , an antifer- romagnetic 3-k type ordering of U moments is identified as one of the lowest energy solutions, in agreement with experiments and recent calculations. For NpO2 , a magnetic multipolar 3-k ordering of triakontadipoles, with a zero net magnetic moment on Np atoms, is found to be one of the most stable solutions. This is in agreement with recent investigations that predict the triakontadipoles to be the hidden order parameter in NpO2 . Also in case of the non-magnetic insulator PuO2 , the ground-state is predicted to be described by a multipolar 1-k ordering of triakontadipoles associated with a magnetization density that integrates to zero on Pu sites.

    Keywords
    strongly correlated electrons, electronic structure calculations, actinides, dioxides
    National Category
    Condensed Matter Physics
    Research subject
    Physics of Matter
    Identifiers
    urn:nbn:se:uu:diva-132065 (URN)
    Available from: 2010-10-13 Created: 2010-10-13 Last updated: 2012-08-01
    8. Itinerant Magnetic Multipole Moments of Rank Five as the Hidden Order in URu2Si2
    Open this publication in new window or tab >>Itinerant Magnetic Multipole Moments of Rank Five as the Hidden Order in URu2Si2
    2009 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 103, no 10, p. 107202-Article in journal (Refereed) Published
    Abstract [en]

    A broken symmetry ground state without any magnetic moments has been   calculated by means of the local-density approximation to density   functional theory plus a local exchange term, the so-called LDA+U   approach, for URu2Si2. The solution is analyzed in terms of a multipole   tensor expansion of the itinerant density matrix and is found to be a   nontrivial magnetic multipole. Analysis and further calculations show   that this type of multipole enters naturally in time reversal breaking   in the presence of large effective spin-orbit coupling and coexists   with magnetic moments for most magnetic actinides.

    National Category
    Physical Sciences
    Identifiers
    urn:nbn:se:uu:diva-98061 (URN)10.1103/PhysRevLett.103.107202 (DOI)000269639800053 ()
    Available from: 2009-02-12 Created: 2009-02-12 Last updated: 2017-12-13Bibliographically approved
    9. Systematic study of the hidden order in URu2Si2 as a multipolar order
    Open this publication in new window or tab >>Systematic study of the hidden order in URu2Si2 as a multipolar order
    (English)Manuscript (preprint) (Other academic)
    National Category
    Condensed Matter Physics
    Research subject
    Physics with spec. in Atomic, Molecular and Condensed Matter Physics
    Identifiers
    urn:nbn:se:uu:diva-172346 (URN)
    Available from: 2012-04-05 Created: 2012-04-05 Last updated: 2012-08-01
    10. The role of triakontadipoles in uranium-based magnetic superconductor materials
    Open this publication in new window or tab >>The role of triakontadipoles in uranium-based magnetic superconductor materials
    (English)Manuscript (preprint) (Other academic)
    Abstract [en]

    We investigate the ground state of the heavy-fermion actinide compounds UPd2Al3 , UNi2Al3 and UPt3 by means of electronic structure calculations including on-site correlation. The results are analyzed through multipole decomposition. In case of UPd2Al3 and UNi2Al3 we stabilize a solution with an antiferromagnetic arrangement of triakontadipoles with ordering vectors, respectively, q = (0, 0, 1/2 ) and q = ( 1/2 , 0, 1/2 ), whose total magnetic moment agrees with the experimental value. In case of UPt3 we identify a solution with a triakontadipole order whose symmetry is not compatible with the presence of a magnetic moment, in accordance with experiments that detect a very small value of the moment. The Fermi surfaces of the multipole dominated solutions have many common features with those obtained by conventional density functional methods. Finally, for URu2Si2 we are able to stabilize a new solution characterized by a q = (0, 0, 1/2 ) ordering of triakontadipoles and a symmetry that forbids a magnetic moment on uranium site. The Fermi surface of this solution is surprisingly similar to the one of the magnetic AF 1-q case in agreement with recent measurements.

    Keywords
    Superconductivity, actinides, hidden order, correlated electrons
    National Category
    Condensed Matter Physics
    Research subject
    Physics of Matter
    Identifiers
    urn:nbn:se:uu:diva-132064 (URN)
    Available from: 2010-10-13 Created: 2010-10-13 Last updated: 2012-08-01
    11. Low spin moment due to hidden multipole order from spin-orbital ordering in LaFeAsO
    Open this publication in new window or tab >>Low spin moment due to hidden multipole order from spin-orbital ordering in LaFeAsO
    2010 (English)In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 81, no 14, p. 140403-Article in journal (Refereed) Published
    Abstract [en]

    An antiferromagnetic (AF) low-moment solution, 0.35 μB / Fe, is found in the case of LaOFeAs for an intermediately strong Coulomb interaction U of 2.75 eV. This solution is stabilized over a large moment solution due to the gain in exchange energy in the formation of large multipoles of the spin magnetization density. The multipoles are of rank four and can be understood as a type of spin-orbital ordering. Parallels can be drawn to the stabilization of the AF order in, e.g., CaCuO2.

    Keywords
    Superconductivity, correlated electrons, electronic structure calculations
    National Category
    Condensed Matter Physics
    Research subject
    Physics of Matter
    Identifiers
    urn:nbn:se:uu:diva-132063 (URN)10.1103/PhysRevB.81.140403 (DOI)000277210200013 ()
    Available from: 2010-10-13 Created: 2010-10-13 Last updated: 2022-01-28Bibliographically approved
    12. Microscopic picture of Co clustering in ZnO
    Open this publication in new window or tab >>Microscopic picture of Co clustering in ZnO
    Show others...
    2009 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 79, no 12, p. 125202-Article in journal (Refereed) Published
    Abstract [en]

    Density functional theory was applied to study the chemical and magnetic interactions between Co atoms doped in ZnO. It was found that the Co impurities tend to form nanoclusters and the interactions between these atoms are antiferromagnetic within the local spin-density approximation (LSDA)+Hubbard U approach. The extracted interatomic exchange parameters agree reasonably well with recent experimental results. We have analyzed and compared the electronic structure obtained using the LSDA and LSDA+U approaches and found that the LSDA+U gives the most reasonable result, highlighting the importance of short-ranged antiferromagnetic interactions due to superexchange.

    Place, publisher, year, edition, pages
    The American Physical Society, 2009
    Keywords
    antiferromagnetic materials, cobalt, density functional theory, II-VI semiconductors, magnetic semiconductors, metal clusters, superexchange interactions, wide band gap semiconductors, zinc compounds
    National Category
    Physical Sciences
    Identifiers
    urn:nbn:se:uu:diva-119891 (URN)10.1103/PhysRevB.79.125202 (DOI)000264769300047 ()
    Available from: 2010-03-02 Created: 2010-03-02 Last updated: 2017-12-12Bibliographically approved
    13. Assessment of the magnetic properties of SrRuO3 using LDA and LDA+DMFT
    Open this publication in new window or tab >>Assessment of the magnetic properties of SrRuO3 using LDA and LDA+DMFT
    Show others...
    (English)Manuscript (preprint) (Other academic)
    National Category
    Condensed Matter Physics
    Research subject
    Physics with spec. in Atomic, Molecular and Condensed Matter Physics
    Identifiers
    urn:nbn:se:uu:diva-172347 (URN)
    Available from: 2012-04-05 Created: 2012-04-05 Last updated: 2012-08-01
    14. Route towards finding large magnetic anisotropy in nanocomposites: Application to a W(1-x)Re(x)/Fe multilayer
    Open this publication in new window or tab >>Route towards finding large magnetic anisotropy in nanocomposites: Application to a W(1-x)Re(x)/Fe multilayer
    Show others...
    2011 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 84, no 9, p. 092401-Article in journal (Refereed) Published
    Abstract [en]

    We suggest here a nanolaminate, 5[Fe]/2[W(x)Re(1-x)] (x = 0.6-0.8), with enhanced magnetic hardness in combination with a large saturation moment. The calculated magnetic anisotropy of this material reaches values of 5.3-7.0 MJ/m(3), depending on alloying conditions. We also propose a recipe in how to identify other novel magnetic materials, such as nanolaminates and multilayers, with large magnetic anisotropy in combination with a high saturation moment.

    National Category
    Physical Sciences
    Identifiers
    urn:nbn:se:uu:diva-159231 (URN)10.1103/PhysRevB.84.092401 (DOI)000294773300001 ()
    Available from: 2011-09-27 Created: 2011-09-26 Last updated: 2017-12-08Bibliographically approved
    15. On the large magnetic anisotropy of Fe2P
    Open this publication in new window or tab >>On the large magnetic anisotropy of Fe2P
    Show others...
    (English)Manuscript (preprint) (Other academic)
    National Category
    Condensed Matter Physics
    Research subject
    Physics with spec. in Atomic, Molecular and Condensed Matter Physics
    Identifiers
    urn:nbn:se:uu:diva-172349 (URN)
    Available from: 2012-04-05 Created: 2012-04-05 Last updated: 2013-03-21
    16. Epitaxial Fe films on ZnSe(001): effect of the substrate surface reconstruction on the magnetic anisotropy
    Open this publication in new window or tab >>Epitaxial Fe films on ZnSe(001): effect of the substrate surface reconstruction on the magnetic anisotropy
    Show others...
    2012 (English)In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 24, no 23, p. 236006-Article in journal (Refereed) Published
    Abstract [en]

    It is well known that Fe films deposited on a c(2 x 2)-reconstructed ZnSe(001) surface show a strong in-plane uniaxial magnetic anisotropy. Here, the effect of the substrate reconstruction on the magnetic anisotropy of Fe has been studied by in situ Brillouin light scattering. We found that the in-plane uniaxial anisotropy is strongly reduced for Fe films grown on a (1 x 1)-unreconstructed ZnSe substrate while the in-plane biaxial one is nearly unaffected by the substrate reconstruction. Calculations of magnetic anisotropy energies within the framework of ab initio density functional theory reveal that the strong suppression of anisotropy at the (1 x 1) interface occurs due to complex atomic relaxations as well as the competing effects originating from magnetocrystalline anisotropy and dipole-dipole interactions. For both sharp and intermixed c(2 x 2) interfaces, the magnetic anisotropy is enhanced compared to the (1 x 1) case due to the further lowering of symmetry. The theoretical results are in agreement with the experimental findings. 

    National Category
    Condensed Matter Physics
    Research subject
    Physics with spec. in Atomic, Molecular and Condensed Matter Physics
    Identifiers
    urn:nbn:se:uu:diva-172350 (URN)10.1088/0953-8984/24/23/236006 (DOI)000304873800028 ()
    Available from: 2012-04-05 Created: 2012-04-05 Last updated: 2022-01-28Bibliographically approved
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  • 30. Grånäs, Oscar
    et al.
    Bultmark, F.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Cricchio, F.
    Nordström, Lars
    Analysis of dynamical exchange and correlation in terms of coupled multipolesManuscript (Other academic)
  • 31.
    Grånäs, Oscar
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Cricchio, F
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Nordström, L
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Systematic study of the hidden order in URu2Si2 as a multipolar orderManuscript (preprint) (Other academic)
  • 32.
    Grånäs, Oscar
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Di Marco, Igor
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Nordström, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Etz, Corina
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Electronic structure, cohesive properties, and magnetism of SrRuO32014In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 90, no 16, p. 165130-Article in journal (Refereed)
    Abstract [en]

    We have performed an extensive test of the ability of density functional theory within several approximations for the exchange-correlation functional, local density approximation + Hubbard U, and local density approximation + dynamic mean field theory to describe magnetic and electronic properties of SrRuO3. We focus on the ferromagnetic phase, illustrating differences between the orthorhombic low-temperature structure versus the cubic high-temperature structure. We assess how magnetism, spectral function, and cohesive properties are affected by methodology, onsite Hubbard U, and double-counting corrections. Further, we compare the impact of the impurity solver on the quasiparticle weight Z, which is in turn compared to experimental results. The spectral functions resulting from the different treatments are also compared to experimental data. Finally, the impact of spin-orbit coupling is studied, allowing us to determine the orbital moments. In the orthorhombic phase, the orbital moments are found to be tilted with respect to the spin moments, emphasizing the importance of taking into account the distortion of the oxygen octahedra.

  • 33.
    Grånäs, Oscar
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Di Marco, Igor
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Thunström, Patrik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Nordström, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Björkman, T.
    Wills, J. M.
    Charge self-consistent dynamical mean-field theory based on the full-potential linear muffin-tin orbital method: Methodology and applications2012In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 55, p. 295-302Article in journal (Refereed)
    Abstract [en]

    Full charge self-consistence (CSC) over the electron density has been implemented into the local density approximation plus dynamical mean-field theory (LDA + DMFT) scheme based on a full-potential linear muffin-tin orbital method (FP-LMTO). Computational details on the construction of the electron density from the density matrix are provided. The method is tested on the prototypical charge-transfer insulator NiO using a simple static Hartree-Fock approximation as impurity solver. The spectral and ground state properties of bcc Fe are then addressed, by means of the spin-polarized T-matrix fluctuation exchange solver (SPTF). Finally the permanent magnet SmCo5 is studied using multiple impurity solvers, SPTF and Hubbard I, as the strength of the local Coulomb interaction on the Sm and Co sites are drastically different. The developed CSC-DMFT method is shown to in general improve on materials properties like magnetic moments, electronic structure and the materials density.

  • 34.
    Grånäs, Oscar
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Dutta, Biswanath
    Ghosh, Subhradip
    Sanyal, Biplab
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    A new first principles approach to calculate phonon spectra of disordered alloys2012In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 24, no 1, p. 015402-Article in journal (Refereed)
    Abstract [en]

    The lattice dynamics in substitutional disordered alloys with constituents having large size differences is driven by strong disorder in masses, inter-atomic force constants and local environments. In this paper, a new first principles approach based on special quasirandom structures and an itinerant coherent potential approximation to compute the phonon spectra of such alloys is proposed and applied to Ni(0.5)Pt(0.5) alloy. The agreement between our results and experiments is found to be much better than for previous models of disorder due to an accurate treatment of the interplay of inter-atomic forces among various pairs of chemical species. This new formalism serves as a potential solution to the longstanding problem of a proper microscopic understanding of lattice dynamical behavior of disordered alloys.

  • 35.
    Grånäs, Oscar
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Harvard University, School of Engineering and Applied Sciences.
    Kolesov, Grigory
    Harvard University, School of Engineering and Applied Sciences.
    Kaxiras, Efthimios
    Harvard University, School of Engineering and Applied Sciences.
    Impact of Vibrations and Electronic Coherence on Electron Transfer in Flat Molecular Wires2017In: MRS Advances, E-ISSN 2059-8521, Vol. 2, no 14, p. 811-816Article in journal (Refereed)
    Abstract [en]

    Electron transfer in molecular wires are of fundamental importance for a range of optoelectronic applications. The impact of electronic coherence and ionic vibrations on transmittance are of great importance to determine the mechanisms, and subsequently the type of wires that are most promising for applications. In this work, we use the real-time formulation of time-dependent density functional theory to study electron transfer through oligo-pphenylenevinylene (OPV) and the recently synthesized carbon bridged counterpart (COPV). A system prototypical of organic photovoltaics is setup by bridging a porphyrin-fullerene dyad, allowing a photo-excited electron to flow between the Zn-porphyrin (ZnP) chromophore and the C60 electron acceptor through the molecular wire. The excited state is described using the fully self-consistent.-SCF method. The state is then propagated in time using the real-time TD-DFT scheme, while describing ionic vibrations with classical nuclei. The charge transferred between porphyrin and C60 is calculated and correlated with the velocity autocorrelation functions of the ions. This provides a microscopic insight to vibrational and tunneling contributions to electron transport in linked porphyrin-fullerene dyads. We elaborate on important details in describing the excited state and trajectory sampling.

  • 36.
    Grånäs, Oscar
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Mocellin, A.
    Brasilia Univ, Inst Phys, Brasilia, DF, Brazil..
    Cardoso, E. S.
    Lab Nacl Luz Sincrotron, Box 6192, BR-13083970 Campinas, SP, Brazil.;Univ Estadual Campinas, Rua Sergio Buarque Holanda 777,Cidade Univ, BR-13083970 Campinas, SP, Brazil..
    Burmeister, Florian
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Caleman, Carl
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics. DESY, Ctr Free Electron Laser Sci, Notkestr 85, DE-22607 Hamburg, Germany..
    Björneholm, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Naves de Brito, A.
    Univ Estadual Campinas, Rua Sergio Buarque Holanda 777,Cidade Univ, BR-13083970 Campinas, SP, Brazil..
    Femtosecond fragmentation of CS2 after sulfur 1s ionization: interplay between Auger cascade decay, charge delocalization, and nuclear motion2020In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 53, no 24, article id 244007Article in journal (Refereed)
    Abstract [en]

    We present a combined experimental and theoretical study of the fragmentation of molecular CS2 after sulfur 1s Auger cascade decay, consisting of electron-multi-ion coincidence spectra of charged fragments and theoretical simulations combining density functional theory and molecular dynamics. On the experimental side, a procedure for a complete determination of all sets of ions formed is described. For many of the fragmentation channels, we observed a higher charge in one of the sulfur atoms than the other atoms. Based on these observations and the theoretical simulations where the time scale of the nuclear motion and decay is taken into account, we propose that KLL Auger decay after the 1s core hole creation, via 2p double hole states, results in highly charged and strongly repulsive states with one localized core hole. These localized core holes are sufficiently long-lived that some will decay after fragmentation of the molecular ion, thereby efficiently impeding charge exchange between the fragments.

  • 37.
    Grånäs, Oscar
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Timneanu, Nicusor
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Eliah Dawod, Ibrahim
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Ragazzon, Davide
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Trygg, Sebastian
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Souvatzis, Petros
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Edvinsson, Tomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences.
    Caleman, Carl
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Femtosecond bond breaking and charge dynamics in ultracharged amino acids2019In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 151, no 14, article id 144307Article in journal (Refereed)
    Abstract [en]

    Historically, structure determination of nanocrystals, proteins, and macromolecules required the growth of high-quality crystals sufficiently large to diffract X-rays efficiently while withstanding radiation damage. The development of the X-ray free-electron laser has opened the path toward high resolution single particle imaging, and the extreme intensity of the X-rays ensures that enough diffraction statistics are collected before the sample is destroyed by radiation damage. Still, recovery of the structure is a challenge, in part due to the partial fragmentation of the sample during the diffraction event. In this study, we use first-principles based methods to study the impact of radiation induced ionization of six amino acids on the reconstruction process. In particular, we study the fragmentation and charge rearrangement to elucidate the time scales involved and the characteristic fragments occurring.

    Download full text (pdf)
    fulltext
  • 38.
    Grånäs, Oscar
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Vaskivskyi, I.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy. Univ Calif San Diego, Ctr Memory & Recording Res, 9500 Gilman Dr, La Jolla, CA 92093 USA..
    Wang, X.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Thunström, Patrik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ghimire, S.
    SLAC Natl Accelerator Lab, Stanford PULSE Inst, 2575 Sand Hill Rd, Menlo Pk, CA 94025 USA..
    Knut, Ronny
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Condensed Matter Physics of Energy Materials.
    Söderström, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Chemical and Bio-Molecular Physics.
    Kjellsson, L.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Turenne, Diego
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, FREIA.
    Engel, R. Y.
    DESY, Dept Photon Sci, Notkestr 85, D-22607 Hamburg, Germany..
    Beye, M.
    DESY, Dept Photon Sci, Notkestr 85, D-22607 Hamburg, Germany..
    Lu, J.
    SLAC Natl Accelerator Lab, Stanford PULSE Inst, 2575 Sand Hill Rd, Menlo Pk, CA 94025 USA..
    Higley, D. J.
    SLAC Natl Accelerator Lab, 2575 Sand Hill Rd, Menlo Pk, CA 94025 USA..
    Reid, A. H.
    SLAC Natl Accelerator Lab, 2575 Sand Hill Rd, Menlo Pk, CA 94025 USA..
    Schlotter, W.
    SLAC Natl Accelerator Lab, 2575 Sand Hill Rd, Menlo Pk, CA 94025 USA..
    Coslovich, G.
    SLAC Natl Accelerator Lab, 2575 Sand Hill Rd, Menlo Pk, CA 94025 USA.;Harvard Univ, John Paulson Sch Engn & Appl Sci, Cambridge, MA 02138 USA..
    Hoffmann, M.
    SLAC Natl Accelerator Lab, 2575 Sand Hill Rd, Menlo Pk, CA 94025 USA..
    Kolesov, G.
    Schissler-Langeheine, C.
    Helmholtz Zent Berlin Mat & Energie GmbH, D-12489 Berlin, Germany..
    Styervoyedov, A.
    Max Planck Inst Mikrostrukturphys, Weinberg 2, Halle, Germany..
    Tancogne-Dejean, N.
    Max Planck Inst Struct & Dynam Matter, Luruper Chaussee 149, D-22761 Hamburg, Germany.;Ctr Free Electron Laser Sci, Sch Sci & Technol, Luruper Chaussee 149, SE-70182 Hamburg, Germany..
    Sentef, M. A.
    Max Planck Inst Struct & Dynam Matter, Luruper Chaussee 149, D-22761 Hamburg, Germany.;Ctr Free Electron Laser Sci, Sch Sci & Technol, Luruper Chaussee 149, SE-70182 Hamburg, Germany..
    Reis, D. A.
    SLAC Natl Accelerator Lab, Stanford PULSE Inst, 2575 Sand Hill Rd, Menlo Pk, CA 94025 USA..
    Rubio, A.
    Max Planck Inst Struct & Dynam Matter, Luruper Chaussee 149, D-22761 Hamburg, Germany.;Ctr Free Electron Laser Sci, Sch Sci & Technol, Luruper Chaussee 149, SE-70182 Hamburg, Germany.;Flatiron Inst, Ctr Computat Quantum Phys, New York, NY 10010 USA..
    Parkin, S. S. P.
    Max Planck Inst Mikrostrukturphys, Weinberg 2, Halle, Germany..
    Karis, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Condensed Matter Physics of Energy Materials.
    Rubensson, J. -e.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Solid State Physics.
    Dürr, Hermann
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, FREIA.
    Ultrafast modification of the electronic structure of a correlated insulator2022In: Physical Review Research, E-ISSN 2643-1564, Vol. 4, no 3, article id L032030Article in journal (Refereed)
    Abstract [en]

    A nontrivial balance between Coulomb repulsion and kinematic effects determines the electronic structure of correlated electron materials. The use of electromagnetic fields strong enough to rival these native microscopic interactions allows us to study the electronic response as well as the time scales and energies involved in using quantum effects for possible applications. We use element-specific transient x-ray absorption spectroscopy and high-harmonic generation to measure the response to ultrashort off-resonant optical fields in the prototypical correlated electron insulator NiO. Surprisingly, fields of up to 0.22 V/angstrom lead to no detectable changes in the correlated Ni 3d orbitals contrary to previous predictions. A transient directional charge transfer is uncovered, a behavior that is captured by first-principles theory. Our results highlight the importance of retardation effects in electronic screening and pinpoints a key challenge in functionalizing correlated materials for ultrafast device operation.

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  • 39.
    Iusan, Diana
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Materials Theory.
    Kabir, Mukul
    Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts.
    Grånäs, Oscar
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Materials Theory.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Materials Theory.
    Sanyal, Biplab
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Materials Theory.
    Microscopic picture of Co clustering in ZnO2009In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 79, no 12, p. 125202-Article in journal (Refereed)
    Abstract [en]

    Density functional theory was applied to study the chemical and magnetic interactions between Co atoms doped in ZnO. It was found that the Co impurities tend to form nanoclusters and the interactions between these atoms are antiferromagnetic within the local spin-density approximation (LSDA)+Hubbard U approach. The extracted interatomic exchange parameters agree reasonably well with recent experimental results. We have analyzed and compared the electronic structure obtained using the LSDA and LSDA+U approaches and found that the LSDA+U gives the most reasonable result, highlighting the importance of short-ranged antiferromagnetic interactions due to superexchange.

  • 40.
    Ji, Shaozheng
    et al.
    KTH Royal Inst Technol, Sch Engn Sci, Mat & Nano Phys, SE-10044 Stockholm, Sweden.;Nankai Univ, Sch Phys, Ultrafast Electron Microscopy Lab, MOE Key Lab Weak Light Nonlinear Photon, Tianjin 300071, Peoples R China..
    Grånäs, Oscar
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Prasad, Amit Kumar
    KTH Royal Inst Technol, Sch Engn Sci, Mat & Nano Phys, SE-10044 Stockholm, Sweden..
    Weissenrieder, Jonas
    KTH Royal Inst Technol, Sch Engn Sci, Mat & Nano Phys, SE-10044 Stockholm, Sweden..
    Influence of strain on an ultrafast phase transition2022In: Nanoscale, ISSN 2040-3364, E-ISSN 2040-3372, Vol. 15, no 1, p. 304-312Article in journal (Refereed)
    Abstract [en]

    The flexibility of 2D materials combined with properties highly sensitive to strain makes strain engineering a promising avenue for manipulation of both structure and function. Here we investigate the influence of strain, associated with microstructural defects, on a photo-induced structural phase transition in Td–WTe2. Above threshold photoexcitation of uniform, non-strained, samples result in an orthorhombic Td to a metastable orthorhombic 1T* phase transition facilitated by shear displacements of the WTe2 layers along the b axis of the material. In samples prepared with wrinkle defects WTe2 continue its trajectory through a secondary transition that shears the unit cell along the c axis towards a metastable monoclinic 1T′ phase. The time scales and microstructural evolution associated with the transition and its subsequent recovery to the 1T* phase is followed in detail by a combination of ultrafast electron diffraction and microscopy. Our findings show how local strain fields can be employed for tailoring phase change dynamics in ultrafast optically driven processes with potential applications in phase change devices.

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  • 41.
    Ji, Shaozheng
    et al.
    KTH Royal Inst Technol, Sch Engn Sci, Mat & Nano Phys, SE-10044 Stockholm, Sweden.
    Grånäs, Oscar
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Rossnagel, Kai
    Christian Albrechts Univ Kiel, Inst Expt & Angew Phys, D-24098 Kiel, Germany;DESY, Ruprecht Haensel Lab, D-22607 Hamburg, Germany.
    Weissenrieder, Jonas
    KTH Royal Inst Technol, Sch Engn Sci, Mat & Nano Phys, SE-10044 Stockholm, Sweden.
    Transient three-dimensional structural dynamics in 1T -TaSe22020In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 101, no 9, article id 094303Article in journal (Refereed)
    Abstract [en]

    We report on thermal and optically driven transitions between the commensurate (C) and incommensurate (IC) charge-density wave (CDW) phases of 1T-TaSe2. Optical excitation results in suppression of the C-CDW on a subpicosecond timescale. The optically driven C to IC transition involves a short-lived (similar to 1 ps) unreconstructed phase. Nucleation of an IC phase stacking order is observed already at similar to 4 ps following photoexcitation. The short timescales involved in establishing the stacking order implies that the nucleation of the IC phase is influenced by the local geometry of the adjacent layers such that the stacking direction of the C phase determines the stacking direction of the IC phase. From this follows that the nucleation of the IC-CDW is inherently three dimensional (3D). We observe the activation of a coherent shear mode in the optically driven transitions to the transiently stabilized unreconstructed phase. The activation mechanism starts with a rapid lifting of the periodic lattice distortions (PLD) of the Ta sublattice which results in formation of local transient velocity disparities in the Se sublattice. The local differences in Se-phonon amplitudes result in noncompensated shear forces between the layers. This is an example of a multistep coherent launching mechanism. The energy of the optically excited electronic state dissipates energy into modes of the PLD through strong electron-phonon coupling. The rapid suppression of the PLD launches the third step, a coherent vibrational shear mode with low dissipation. The results highlight the importance in considering the 3D nature of the CDWs in the analysis of both structure and dynamics in transition-metal dichalcogenides.

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  • 42.
    Ji, Shaozheng
    et al.
    KTH Royal Inst Technol, Sch Engn Sci, Mat & Nano Phys, SE-10044 Stockholm, Sweden..
    Grånäs, Oscar
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Weissenrieder, Jonas
    KTH Royal Inst Technol, Sch Engn Sci, Mat & Nano Phys, SE-10044 Stockholm, Sweden..
    Manipulation of Stacking Order in Td-WTe2 by Ultrafast Optical Excitation2021In: ACS Nano, ISSN 1936-0851, E-ISSN 1936-086X, Vol. 15, no 5, p. 8826-8835Article in journal (Refereed)
    Abstract [en]

    Subtle changes in stacking order of layered transition metal dichalcogenides may have profound influence on the electronic and optical properties. The intriguing electronic properties of Td-WTe2 can be traced to the break of inversion symmetry resulting from the ground-state stacking sequence. Strategies for perturbation of the stacking order are actively pursued for intentional tuning of material properties, where optical excitation is of specific interest since it holds the potential for integration of ultrafast switches in future device designs. Here we investigate the structural response in Td-WTe2 following ultrafast photoexcitation by time-resolved electron diffraction. A 0.23 THz shear phonon, involving layer displacement along the b axis, was excited by a 515 nm laser pulse. Pump fluences in excess of a threshold of similar to 1 mJ/cm(2) result in formation, with an similar to 5 ps time constant, of a new stacking order by layer displacement along the b axis in the direction toward the centrosymmetric 1T* phase. The shear displacement of the layers increases with pump fluence until saturation at similar to 8 pm. We demonstrate that the excitation of the shear phonon and the stabilization of the metastable phase are decoupled when using an optical pump as evidenced by observation of a transition also in samples with a pinned shear phonon. The results are compared to dynamic first-principles simulations and the transition is interpreted in terms of a mechanism where transient local disorder is prominent before settling at the atomic positions of the metastable phase. This interpretation is corroborated by results from diffuse scattering. The correlation between excitation of intralayer vibrations and interlayer interaction demonstrates the importance of including both short- and long-range interactions in an accurate description of how optical fields can be employed to manipulate the stacking order in 2-dimensional transition metal dichalcogenides.

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  • 43.
    Kolesov, Grigory
    et al.
    Harvard Univ, John A Paulson Sch Engn & Appl Sci, Cambridge, MA 02138 USA..
    Grånäs, Oscar
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Harvard Univ, John A Paulson Sch Engn & Appl Sci, Cambridge, MA 02138 USA..
    Hoyt, Robert
    Harvard Univ, Dept Phys, Cambridge, MA 02138 USA..
    Vinichenko, Dmitry
    Harvard Univ, Dept Chem & Chem Biol, Cambridge, MA 02138 USA..
    Kaxiras, Efthimios
    Harvard Univ, John A Paulson Sch Engn & Appl Sci, Cambridge, MA 02138 USA.;Harvard Univ, Dept Phys, Cambridge, MA 02138 USA..
    Real-Time TD-DFT with Classical Ion Dynamics: Methodology and Applications2016In: Journal of Chemical Theory and Computation, ISSN 1549-9618, E-ISSN 1549-9626, Vol. 12, no 2, p. 466-476Article in journal (Refereed)
    Abstract [en]

    We present a method for real-time propagation of electronic wave functions, within time-dependent density functional theory (RT-TDDFT), coupled to ionic motion through mean-field classical dynamics. The goal of our method is to treat large systems and complex processes, in particular photocatalytic reactions and electron transfer events on surfaces and thin films. Due to the complexity of these processes, computational approaches are needed to provide insight into the underlying physical mechanisms and are therefore crucial for the rational design of new materials. Because of the short time step required for electron propagation (of order similar to 10 attoseconds), these simulations are computationally very demanding. Our methodology is based on numerical atomic-orbital-basis sets for computational efficiency. In the computational package, to which we refer as TDAP-2.0 (Time-evolving Deterministic Atom Propagator), we have implemented a number of important features and analysis tools for more accurate and efficient treatment of large, complex systems and time scales that reach into a fraction of a picosecond. We showcase the capabilities of our method using four different examples: (i) photodissociation into radicals of opposite spin, (ii) hydrogen adsorption on aluminum surfaces, (iii) optical absorption of spin-polarized organic molecule containing a metal ion, and (iv) electron transfer in a prototypical dye sensitized solar cell.

  • 44.
    Kvashnin, Yaroslav O.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Grånäs, Oscar
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Di Marco, Igor
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Katsnelson, M. I.
    Lichtenstein, A. I.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Exchange parameters of strongly correlated materials: Extraction from spin-polarized density functional theory plus dynamical mean-field theory2015In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 91, no 12, article id 125133Article in journal (Refereed)
    Abstract [en]

    In this paper we present an accurate numerical scheme for extracting interatomic exchange parameters (J(ij)) of strongly correlated systems, based on first-principles full-potential electronic structure theory. The electronic structure is modeled with the help of a full-potential linear muffin-tin orbital method. The effects of strong electron correlations are considered within the charge self-consistent density functional theory plus dynamical mean-field theory. The exchange parameters are then extracted using the magnetic force theorem; hence all the calculations are performed within a single computational framework. The method allows us to investigate how the Jij parameters are affected by dynamical electron correlations. In addition to describing the formalism and details of the implementation, we also present magnetic properties of a few commonly discussed systems, characterized by different degrees of electron localization. In bcc Fe, treated as a moderately correlated metal, we found a minor renormalization of the Jij interactions once the dynamical correlations are introduced. However, generally, if the magnetic coupling has several competing contributions from different orbitals, the redistribution of the spectral weight and changes in the exchange splitting of these states can lead to a dramatic modification of the total interaction parameter. In NiO we found that both static and dynamical mean-field results provide an adequate description of the exchange interactions, which is somewhat surprising given the fact that these two methods result in quite different electronic structures. By employing the Hubbard-I approximation for the treatment of the 4f states in hcp Gd we reproduce the experimentally observed multiplet structure. The calculated exchange parameters result in being rather close to the ones obtained by treating the 4f electrons as noninteracting core states.

  • 45.
    Panda, Swarup K.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Di Marco, Igor
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Grånäs, Oscar
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Harvard, Sch Engn & Appl Sci, 29 Oxford St, Cambridge, MA 02138 USA.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Fransson, Jonas
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Electronic and magnetic properties of single Fe atoms on a CuN surface: Effects of electron correlations2016In: PHYSICAL REVIEW B, ISSN 2469-9950, Vol. 93, no 14, article id 140101Article in journal (Refereed)
    Abstract [en]

    The electronic structure and magnetic properties of a single Fe adatom on a CuN surface have been studied using density functional theory in the local spin density approximation (LSDA), the LSDA+U approach, and the local density approximation plus dynamical mean-field theory (LDA+DMFT). The impurity problem in LDA+DMFT is solved through exact diagonalization and in the Hubbard-I approximation. The comparison of the one-particle spectral functions obtained from LSDA, LSDA+U, and LDA+DMFT show the importance of dynamical correlations for the electronic structure of this system. Most importantly, we focused on the magnetic anisotropy and found that neither LSDA nor LSDA+U can explain the measured high values of the axial and transverse anisotropy parameters. Instead, the spin excitation energies obtained from our LDA+DMFT approach with exact diagonalization agree significantly better with experimental data. This affirms the importance of treating fluctuating magnetic moments through a realistic many-body treatment when describing this class of nanomagnetic systems. Moreover, it facilitates insight to the role of the hybridization with surrounding orbitals.

  • 46.
    Peters, L.
    et al.
    Radboud Univ Nijmegen, Inst Mol & Mat, NL-6525 AJ Nijmegen, Netherlands..
    Di Marco, Igor
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Grånäs, Oscar
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Sasioglu, E.
    Forschungszentrum Julich, Peter Grunberg Inst, D-52425 Julich, Germany.;Forschungszentrum Julich, Inst Adv Simulat, D-52425 Julich, Germany.;JARA, D-52425 Julich, Germany..
    Altun, A.
    Fatih Univ, Dept Phys, TR-34500 Istanbul, Turkey..
    Rossen, S.
    Radboud Univ Nijmegen, Inst Mol & Mat, NL-6525 AJ Nijmegen, Netherlands.;Forschungszentrum Julich, Peter Grunberg Inst, D-52425 Julich, Germany.;Forschungszentrum Julich, Inst Adv Simulat, D-52425 Julich, Germany.;JARA, D-52425 Julich, Germany..
    Friedrich, C.
    Forschungszentrum Julich, Peter Grunberg Inst, D-52425 Julich, Germany.;Forschungszentrum Julich, Inst Adv Simulat, D-52425 Julich, Germany.;JARA, D-52425 Julich, Germany..
    Bluegel, S.
    Forschungszentrum Julich, Peter Grunberg Inst, D-52425 Julich, Germany.;Forschungszentrum Julich, Inst Adv Simulat, D-52425 Julich, Germany.;JARA, D-52425 Julich, Germany..
    Katsnelson, M. I.
    Radboud Univ Nijmegen, Inst Mol & Mat, NL-6525 AJ Nijmegen, Netherlands..
    Kirilyuk, A.
    Radboud Univ Nijmegen, Inst Mol & Mat, NL-6525 AJ Nijmegen, Netherlands..
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Correlation effects and orbital magnetism of Co clusters2016In: PHYSICAL REVIEW B, ISSN 2469-9950, Vol. 93, no 22, article id 224428Article in journal (Refereed)
    Abstract [en]

    Recent experiments on isolated Co clusters have shown huge orbital magnetic moments in comparison with their bulk and surface counterparts. These clusters hence provide the unique possibility to study the evolution of the orbital magnetic moment with respect to the cluster size and how competing interactions contribute to the quenching of orbital magnetism. We investigate here different theoretical methods to calculate the spin and orbital moments of Co clusters, and assess the performances of the methods in comparison with experiments. It is shown that density-functional theory in conventional local density or generalized gradient approximations, or even with a hybrid functional, severely underestimates the orbital moment. As natural extensions/corrections, we considered the orbital polarization correction, the LDA+U approximation as well as the LDA+DMFT method. Our theory shows that of the considered methods, only the LDA+DMFT method provides orbital moments in agreement with experiment, thus emphasizing the importance of dynamic correlations effects for determining fundamental magnetic properties of magnets in the nanosize regime.

  • 47. Prasad, Amit Kumar
    et al.
    Esteban-Puyuelo, Raquel
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Maldonado, Pablo
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ji, Shaozheng
    Sanyal, Biplab
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Grånäs, Oscar
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Weissenrieder, Jonas
    Visualizing nonequlibrium atomic motion and energy transfer in SnSeManuscript (preprint) (Other academic)
  • 48.
    Prasad, Amit Kumar
    et al.
    KTH Royal Inst Technol, Sch Engn Sci, Mat & Nano Phys, SE-10044 Stockholm, Sweden..
    Sebesta, Jakub
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Esteban-Puyuelo, Raquel
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Maldonado, Pablo
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ji, Shaozheng
    KTH Royal Inst Technol, Sch Engn Sci, Mat & Nano Phys, SE-10044 Stockholm, Sweden..
    Sanyal, Biplab
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Grånäs, Oscar
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Weissenrieder, Jonas
    KTH Royal Inst Technol, Sch Engn Sci, Mat & Nano Phys, SE-10044 Stockholm, Sweden..
    Nonequilibrium Phonon Dynamics and Its Impact on the Thermal Conductivity of the Benchmark Thermoelectric Material SnSe2023In: ACS Nano, ISSN 1936-0851, E-ISSN 1936-086X, Vol. 17, no 21, p. 21006-21017Article in journal (Refereed)
    Abstract [en]

    Thermoelectric materials play a vital role in the pursuit of a sustainable energy system by allowing the conversion of waste heat to electric energy. Low thermal conductivity is essential to achieving high-efficiency conversion. The conductivity depends on an interplay between the phononic and electronic properties of the nonequilibrium state. Therefore, obtaining a comprehensive understanding of nonequilibrium dynamics of the electronic and phononic subsystems as well as their interactions is key for unlocking the microscopic mechanisms that ultimately govern thermal conductivity. A benchmark material that exhibits ultralow thermal conductivity is SnSe. We study the nonequilibrium phonon dynamics induced by an excited electron population using a framework combining ultrafast electron diffuse scattering and nonequilibrium kinetic theory. This in-depth approach provides a fundamental understanding of energy transfer in the spatiotemporal domain. Our analysis explains the dynamics leading to the observed low thermal conductivity, which we attribute to a mode-dependent tendency to nonconservative phonon scattering. The results offer a penetrating perspective on energy transport in condensed matter with far-reaching implications for rational design of advanced materials with tailored thermal properties.

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  • 49.
    Ryan, Sinead A.
    et al.
    Univ Colorado Boulder, JILA, 440 UCB, Boulder, CO 80309 USA..
    Johnsen, Peter C.
    Univ Colorado Boulder, JILA, 440 UCB, Boulder, CO 80309 USA..
    Elhanoty, Mohamed F.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Grafov, Anya
    Univ Colorado Boulder, JILA, 440 UCB, Boulder, CO 80309 USA..
    Li, Na
    Univ Colorado Boulder, JILA, 440 UCB, Boulder, CO 80309 USA..
    Delin, Anna
    AlbaNova Univ Ctr, KTH Royal Inst Technol, Sch Engn Sci, Dept Appl Phys, SE-10691 Stockholm, Sweden.;KTH Royal Inst Technol, Swedish E Sci Res Ctr SeRC, SE-10044 Stockholm, Sweden.;Wallenberg Initiat Mat Sci Sustainabil, S-75121 Uppsala, Sweden..
    Markou, Anastasios
    Univ Ioannina, Phys Dept, Ioannina 45110, Greece.;Max Planck Inst Chem Phys Solids, D-01187 Dresden, Germany..
    Lesne, Edouard
    Max Planck Inst Chem Phys Solids, D-01187 Dresden, Germany..
    Felser, Claudia
    Max Planck Inst Chem Phys Solids, D-01187 Dresden, Germany..
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Wallenberg Initiat Mat Sci Sustainabil, S-75121 Uppsala, Sweden..
    Kapteyn, Henry C.
    Univ Colorado Boulder, JILA, 440 UCB, Boulder, CO 80309 USA.;KMLabs Inc, Boulder, CO USA..
    Grånäs, Oscar
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Murnane, Margaret M.
    Univ Colorado Boulder, JILA, 440 UCB, Boulder, CO 80309 USA..
    Optically controlling the competition between spin flips and intersite spin transfer in a Heusler half-metal on sub-100-fs time scales2023In: Science Advances, E-ISSN 2375-2548, Vol. 9, no 45, article id eadi1428Article in journal (Refereed)
    Abstract [en]

    The direct manipulation of spins via light may provide a path toward ultrafast energy-efficient devices. However, distinguishing the microscopic processes that can occur during ultrafast laser excitation in magnetic alloys is challenging. Here, we study the Heusler compound Co2MnGa, a material that exhibits very strong light-induced spin transfers across the entire M-edge. By combining the element specificity of extreme ultraviolet high-harmonic probes with time-dependent density functional theory, we disentangle the competition between three ultrafast light-induced processes that occur in Co2MnGa: same-site Co-Co spin transfer, intersite Co-Mn spin transfer, and ultrafast spin flips mediated by spin-orbit coupling. By measuring the dynamic magnetic asymmetry across the entire M-edges of the two magnetic sublattices involved, we uncover the relative dominance of these processes at different probe energy regions and times during the laser pulse. Our combined approach enables a comprehensive microscopic interpretation of laser-induced magnetization dynamics on time scales shorter than 100 femtoseconds.

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  • 50.
    Sanyal, Biplab
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Materials Theory.
    Grånäs, Oscar
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Materials Theory.
    Knut, Ronny
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Coleman, V. A
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Materials Theory.
    Thunström, Patrik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Materials Theory.
    Iusan, Diana M
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Materials Theory.
    Karis, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Materials Theory.
    Westin, Gunnar
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry.
    Electronic structure of Co doped ZnO: Theory and experiment2008In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 103, no 7, p. 07D130-Article in journal (Refereed)
    Abstract [en]

    We have studied the electronic structure of Co doped ZnO by theory and experiment. Photoelectron and x-ray absorption spectroscopy experiments were performed on 5% Co doped ZnO thin films. The results show that Co-3d states lie in the valence band and hybridize considerably with O-2p states. These results compare qualitatively with our density functional calculations combined with a Hubbard approach to include strong electron correlations within the Co-3d state.

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