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  • 1.
    Alekseev, A. Yu
    et al.
    Belarusian State Univ Informat & Radioelect, P Browka 6, Minsk 220013, BELARUS.
    Chernykh, A. G.
    Belarusian State Univ Informat & Radioelect, P Browka 6, Minsk 220013, BELARUS.
    Filonov, A. B.
    Belarusian State Univ Informat & Radioelect, P Browka 6, Minsk 220013, BELARUS.
    Migas, D. B.
    Belarusian State Univ Informat & Radioelect, P Browka 6, Minsk 220013, BELARUS;Natl Res Nucl Univ MEPhI, Moscow Engn Phys Inst, Kashirskoe Shosse 31, Moscow 115409, Russia.
    Skorodumova, Natalia V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Multiscale Materials Modelling, Department of Materials and Engineering, Royal Institute of Technology (KTH), SE-10044 Stockholm, Sweden.
    Stability of 2D Alkaline-Earth Metal Silicides, Germanides and Stannides2019In: International Journal of Nanoscience, ISSN 0219-581X, Vol. 18, no 3-4, article id 1940013Article in journal (Refereed)
    Abstract [en]

    By means of ab initio calculations, we have estimated stability of 2D Me2X (Me = Mg, Ca, Sr, Ba and X = Si, Ge, Sn) in the T and Td phases, which are similar to the ones of 2D transition metal chalcogenides, in addition to their phonon spectra. The T phase is found to be more stable for 2D Ca2X, Sr2X and Ba2X, whereas the Td phase is predicted to be the ground state for 2D Mg2X. We have also discussed that imaginary frequencies in the calculated phonon spectra of 2D Me2X, which appeared in the vicinity of the Gamma point, were not necessarily associated with the dynamic instability.

  • 2. Al-Zoubi, N.
    et al.
    Skorodumova, Natalia V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Medvedeva, A.
    Andersson, J.
    Nilson, G.
    Johansson, Börje
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Vitos, Levente
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Tetragonality of carbon-doped ferromagnetic iron alloys: A first-principles study2012In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 85, no 1, p. 014112-Article in journal (Refereed)
    Abstract [en]

    Using density-functional theory in combination with the exact muffin-tin orbital (EMTO) method and coherent potential approximation, we investigate the alloying effect on the tetragonality of Fe-C solid solution forming the basis of steels. In order to assess the accuracy of our approach, first we perform a detailed study of the performance of the EMTO method for the Fe(16)C(1) binary system by comparing the EMTO results to those obtained using the projector augmented wave method. In the second step, we introduce different substitutional alloying elements (Al, Cr, Co, Ni) into the Fe matrix and study their impact on the structural parameters. We demonstrate that a small amount of Al, Co, and Ni enhances the tetragonal lattice ratio of Fe(16)C(1) whereas Cr leaves the ratio almost unchanged. The obtained trends are correlated with the single-crystal elastic parameters calculated for carbon-free alloys.

  • 3. Amft, M.
    et al.
    Walle, L. E.
    Ragazzon, Davide
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Borg, A.
    Uvdal, P.
    Skorodumova, Natalia V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Sandell, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    A Molecular Mechanism for the Water-Hydroxyl Balance during Wetting of TiO22013In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 117, no 33, p. 17078-17083Article in journal (Refereed)
    Abstract [en]

    We show that the formation of the wetting layer and the experimentally observed continuous shift of the H2O-OH balance toward molecular water at increasing coverage on a TiO2(110) surface can be rationalized on a molecular level. The mechanism is based on the initial formation of stable hydroxyl pairs, a repulsive interaction between these pairs, and an attractive interaction with respect to water molecules. The experimental data are obtained by synchrotron radiation photoelectron spectroscopy and interpreted with the aid of density functional theory calculations and Monte Carlo simulations.

  • 4.
    Amft, Martin
    et al.
    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, Chemistry, Department of Materials Chemistry, Inorganic Chemistry.
    Skorodumova, Natalia V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Thermally Excited Vibrations in Copper, Silver, and Gold Trimers and Enhanced Binding of CO2010In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126Article in journal (Other academic)
  • 5.
    Amft, Martin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Johansson, Börje
    Skorodumova, Natalia V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Influence of the cluster dimensionality on the binding behavior of CO and O(2) on Au(13)2012In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 136, no 2, p. 024312-Article in journal (Refereed)
    Abstract [en]

    We present an ab initio density functional theory study of the binding behavior of CO and O(2) molecules to two-and three-dimensional isomers of Au(13) in order to investigate the potential catalytic activity of this cluster towards low-temperature CO oxidation. First, we scanned the potential energy surface of Au(13) and studied the effect of spin-orbit coupling on the relative stabilities of the 21 isomers we identified. While spin-orbit coupling increases the stability of the three-dimensional more than the two-dimensional isomers, the ground state structure at 0 K remains planar. Second, we systematically studied the binding of CO and O(2) molecules onto the planar and three-dimensional structures lowest in energy. We find that the isomer dimensionality has little effect on the binding of CO to Au(13). O(2), on the other hand, binds significantly to the three-dimensional isomer only. The simultaneous binding of multiple CO molecules decreases the binding energy per molecule. Still, the CO binding remains stronger than the O(2) binding. We did not find a synergetic effect due to the co-adsorption of both molecular species. On the three-dimensional isomer, we find O(2) dissociation to be exothermic with an dissociation barrier of 1.44 eV.

  • 6.
    Amft, Martin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Lebègue, Sébastien
    Laboratoire de Cristallographie, Résonance Magnétique et Modélisations, Institut Jean Barriol, Nancy Université, Vandoeuvre-lès-Nancy, France.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Skorodumova, Natalia V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Adsorption of Cu, Ag, and Au atoms on graphene including van der Waals interactions2011In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 23, no 39, article id 395001Article in journal (Refereed)
    Abstract [en]

    We performed a systematic density functional (DF) study of the adsorption of copper, silver, and gold adatoms on pristine graphene, especially accounting for van der Waals (vdW) interactions by the vdW-DF and PBE + D2 methods. In particular, we analyze the preferred adsorption site (among top, bridge, and hollow positions) together with the corresponding distortion of the graphene sheet and identify diffusion paths. Both vdW schemes show that the coinage metal atoms do bind to the graphene sheet and that in some cases the buckling of the graphene layer can be significant. Only the results for silver are qualitatively at variance with those obtained with the generalized gradient approximation, which gives no binding in this case. However in all three cases, we observe some quantitative differences between the vdW-DF and PBE + D2 methods. For instance the adsorption energies calculated with the PBE + D2 method are systematically higher than the ones obtained with vdW-DF. Moreover, the equilibrium distances computed with PBE + D2 are shorter than those calculated with the vdW-DF method.

  • 7.
    Amft, Martin
    et al.
    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.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Skorodumova, Natalia
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Small gold clusters on graphene, their mobility and clustering: a DFT study2011In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 23, no 20, p. 205301-Article in journal (Refereed)
    Abstract [en]

    Motivated by the experimentally observed high mobility of gold atoms on graphene and their tendency to form nanometer-sized clusters, we present a density functional theory study of the ground state structures of small gold clusters on graphene, their mobility and clustering. Our detailed analysis of the electronic structures identifies the opportunity to form strong gold-gold bonds and the graphene-mediated interaction of the pre-adsorbed fragments as the driving forces behind gold's tendency to aggregate on graphene. While clusters containing up to three gold atoms have one unambiguous ground state structure, both gas phase isomers of a cluster with four gold atoms can be found on graphene. In the gas phase the diamond-shaped Au-4(D) cluster is the ground state structure, whereas the Y-shaped Au-4(Y) becomes the actual ground state when adsorbed on graphene. As we show, both clusters can be produced on graphene by two distinct clustering processes. We also studied in detail the stepwise formation of a gold dimer out of two pre-adsorbed adatoms, as well as the formation of Au-3. All reactions are exothermic and no further activation barriers, apart from the diffusion barriers, were found. The diffusion barriers of all studied clusters range from 4 to 36 meV only, and are substantially exceeded by the adsorption energies of -0.1 to -0.59 eV. This explains the high mobility of Au1-4 on graphene along the C-C bonds.

  • 8.
    Amft, Martin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Skorodumova, Natalia V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Catalytic activity of small MgO-supported Au clusters towards CO oxidation: A density functional study2010In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 81, no 19, p. 195443-Article in journal (Refereed)
    Abstract [en]

    In order to explain the experimentally found catalytic characteristics of Au1-4 /MgO (100) we have performed a comprehensive density functional study of these systems and their ability to (co)adsorb CO and O2 molecules. Starting from the carefully determined ground-state structures we have analyzed binding mechanisms, the influence of spin-orbit coupling, and charge redistributions in Au1-4 /MgO+CO (O2). Experimentally Au1,2 /MgO were found to be inactive under a mixed atmosphere. We show that O2 strongly binds to Au1 /MgO that prevents coadsorption. Although a catalytic reaction cycle towards CO oxidation, analogous to the gas phase reaction involving Au 2-, is energetically possible for Au2 /MgO, the cluster will get blocked by a strongly bound CO. On the other hand, the catalytic activity of Au3,4 /MgO could be explained by their ability to coadsorb CO and O2, hence indicating the occurrence of a Langmuir- Hinshelwood-type reaction mechanism for these clusters.

  • 9.
    Amft, Martin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Skorodumova, Natalia V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Does H2O improve the catalytic activity of Au1−4/MgO towards CO oxidation?2010In: Journal of Catalysis, ISSN 0021-9517, E-ISSN 1090-2694Article in journal (Other academic)
  • 10.
    Amft, Martin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Skorodumova, Natalia V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    The relative stability of Au13 isomers and their potential for O2 dissociationManuscript (preprint) (Other academic)
  • 11. Andersson, D. A.
    et al.
    Simak, S. I.
    Johansson, Börje
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Abrikosov, I. A.
    Skorodumova, Natalia V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Modeling of CeO2, Ce2O3, and CeO2-x in the LDA plus U formalism2007In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 75, no 3, p. 035109-Article in journal (Refereed)
    Abstract [en]

    The electronic structure and thermodynamic properties of CeO2 and Ce2O3 have been studied from first principles by the all-electron projector-augmented-wave (PAW) method, as implemented in the ab initio total-energy and molecular-dynamics program VASP (Vienna ab initio simulation package). The local density approximation (LDA)+U formalism has been used to account for the strong on-site Coulomb repulsion among the localized Ce 4f electrons. We discuss how the properties of CeO2 and Ce2O3 are affected by the choice of U as well as the choice of exchange-correlation potential, i.e., the local density approximation or the generalized gradient approximation. Further, reduction of CeO2, leading to formation of Ce2O3 and CeO2-x, and its dependence on U and exchange-correlation potential have been studied in detail. Our results show that by choosing an appropriate U it is possible to consistently describe structural, thermodynamic, and electronic properties of CeO2, Ce2O3, and CeO2-x, which enables modeling of redox processes involving ceria-based materials.

  • 12. Andersson, D. A.
    et al.
    Simak, S. I.
    Skorodumova, Natalia V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Abrikosov, I. A.
    Johansson, Börje
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Redox properties of CeO2-MO2 (M=Ti, Zr, Hf, or Th) solid solutions from first principles calculations2007In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 90, no 3, p. 031909-Article in journal (Refereed)
    Abstract [en]

    The authors have used density functional theory calculations to investigate how the redox thermodynamics and kinetics of CeO2 are influenced by forming solid solutions with TiO2, ZrO2, HfO2, and ThO2. Reduction is facilitated by dissolving TiO2 (largest improvement), HfO2, or ZrO2 (least improvement), while ThO2 makes reduction slightly more difficult. The migration barrier is much lower in the neighborhood of a Ti (largest decrease), Hf, or Zr (least decrease), while the binding energy of solute ions and vacancies increases in the same sequence. They rationalize the properties of ceria solid solutions in terms of defect cluster relaxations.

  • 13. Andersson, D. A.
    et al.
    Simak, S. I.
    Skorodumova, Natalia V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Condensed Matter Theory.
    Abrikosov, I. A.
    Johansson, Börje
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Condensed Matter Theory.
    Theoretical study of CeO2 doped with tetravalent ions2007In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 76, no 17, p. 174119-Article in journal (Refereed)
    Abstract [en]

    We have used density functional theory calculations within the LDA+U formulation to investigate how small amounts of dissolved SiO2, GeO2, SnO2, or PbO2 affect the redox thermodynamics of ceria (CeO2). Compared to pure ceria, reduction is facilitated and the reducibility increases in the sequence of CeO2-SnO2, CeO2-GeO2, and CeO2-SiO2, which correlates with the decrease of the ionic radii of the solutes. For low solute concentrations, there is an inverse relation between high reducibility and the solution energy of tetravalent solutes. CeO2-PbO2 is unique in the sense that the initial reduction occurs by Pb(IV)double right arrow Pb(II) instead of the usual Ce(IV)double right arrow Ce(III) reaction. Among the investigated ceria compounds, CeO2-PbO2 has the lowest reduction energy and rather low solution energy. We have studied how the solution and reduction energies depend on the concentration of Si, Ge, Sn, Pb, Ti, Zr, Hf, and Th solute ions. While the solution energy increases monotonously with concentration, the reduction energy first decreases, as compared to pure ceria (except for Th, which exhibits a small increase), and with further increase of solute concentration, it either remains almost constant (Zr, Hf, and Th) or slightly increases (Ti, Si, Ge, and Sn).

  • 14. Andersson, David
    et al.
    Simak, Sergei
    Skorodumova, Natalia
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Abrikosov, Igor
    Johansson, Börje
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Optimization of ionic conductivity in doped ceria2006In: Proc Natl. Acad. Sci. USA, Vol. 103, p. 3495-Article in journal (Refereed)
  • 15. Arapan, Sergiu
    et al.
    Simak, Sergei I.
    Skorodumova, Natalia V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Volume-dependent electron localization in ceria2015In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 91, no 12, article id 125108Article in journal (Refereed)
    Abstract [en]

    We have performed a numerical study of the process of electron localization in reduced ceria. Our results show that different localized charge distributions can be attained in a bulk system by varying the lattice parameter. We demonstrate that the effect of electron localization is mainly determined by lattice relaxation and an accurate account for the effects of electronic correlation is necessary to achieve localized charge distribution.

  • 16.
    Arapan, Sergiu
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Materials Theory.
    Skorodumova, Natalia V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Materials Theory.
    Determination of the Structural Parameters of an Incommensurate Phase from First Principles: The Case of Sc-II2009In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 102, no 8, p. 085701-Article in journal (Refereed)
    Abstract [en]

    We propose a procedure to accurately describe the structural parameters of an incommensurate phase using ab initio methods by approximating it with a set of analogous commensurate supercells. We apply this approach to obtain the structural parameters of the Sc-II phase, which has recently been identified as a complex incommensurate structure similar to Sr-V. The calculated incommensurate ratio gamma, lattice parameters, and Wyckoff positions of Sc-II are in excellent agreement with the available experimental data. Our results show that gamma increases with pressure up to 60 GPa approaching but never reaching the commensurate value 4/3. Hence calculations do not confirm the prediction made based on the reanalyzing of experimental data. When pressure exceeds 70 GPa, gamma shows a sharp decrease that might be considered as the precursor of a new structural phase transition.

  • 17. Belonoshko, A. B.
    et al.
    Davis, S.
    Skorodumova, Natalia V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Lundow, P. H.
    Rosengren, A.
    Johansson, Börje
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Properties of the fcc Lennard-Jones crystal model at the limit of superheating2007In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 76, no 6, p. 064121-Article in journal (Refereed)
    Abstract [en]

    The face-centered-cubic (fcc) Lennard-Jones (LJ) model can be considered as a representative model of a simple solid. We investigate the mechanism of melting at the limit of superheating in the fcc LJ solid by means of the procedure recently developed by us [Phys. Rev. B 73, 012201 (2006)]. Insight into the mechanism of melting was gained by studying diffusion and defects in the fcc LJ solid by means of molecular dynamics simulations. We found that the limit of superheating achieved by us is likely to be the highest so far. We also found that the size of the cluster which ignites the melting is very small (down to five to six atoms, depending on the size of the supercell) and closely correlates with the linear size of a supercell when the number of atoms varies between 500 and 13 500.

  • 18. Belonoshko, A. B.
    et al.
    Isaev, E. I.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Skorodumova, Natalia V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Johansson, Börje
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Stability of the body-centered-tetragonal phase of Fe at high pressure: Ground-state energies, phonon spectra, and molecular dynamics simulations2006In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 74, no 21, p. 214102-Article in journal (Refereed)
    Abstract [en]

    It is well established that at a pressure of several megabars and low temperature Fe is stable in the hexagonal-close-packed (hcp) phase. However, there are indications that on heating a high-pressure hcp phase of Fe transforms to a less dense (open structure) phase. Two phases have been suggested as candidates for these high-temperature stable phases: namely, body-centered-cubic and body-centered-tetragonal (bct) phases. We performed first-principles molecular dynamics and phonon analysis of the bct Fe phase and demonstrated its dynamical instability. This allows us to dismiss the existence of the bct Fe phase under the high-pressure high-temperature conditions of the Earth's inner core.

  • 19. Belonoshko, Anatoly B.
    et al.
    Skorodumova, Natalia V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Davis, Sergio
    Osiptsov, Alexander N.
    Rosengren, Anders
    Johansson, Börje
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Origin of the low rigidity of the Earth's inner core2007In: Science, ISSN 0036-8075, E-ISSN 1095-9203, Vol. 316, no 5831, p. 1603-1605Article in journal (Refereed)
    Abstract [en]

    Earth's solid-iron inner core has a low rigidity that manifests itself in the anomalously low velocities of shear waves as compared to shear wave velocities measured in iron alloys. Normally, when estimating the elastic properties of a polycrystal, one calculates an average over different orientations of a single crystal. This approach does not take into account the grain boundaries and defects that are likely to be abundant at high temperatures relevant for the inner core conditions. By using molecular dynamics simulations, we show that, if defects are considered, the calculated shear modulus and shear wave velocity decrease dramatically as compared to those estimates obtained from the averaged single-crystal values. Thus, the low shear wave velocity in the inner core is explained.

  • 20. Belonoshko, Anatoly B.
    et al.
    Skorodumova, Natalia V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Rosengren, Anders
    Johansson, Börje
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Elastic anisotropy of Earth's inner core2008In: Science, ISSN 0036-8075, E-ISSN 1095-9203, Vol. 319, no 5864, p. 797-800Article in journal (Refereed)
    Abstract [en]

    Earth's solid- iron inner core is elastically anisotropic. Sound waves propagate faster along Earth's spin axis than in the equatorial plane. This anisotropy has previously been explained by a preferred orientation of the iron alloy hexagonal crystals. However, hexagonal iron becomes increasingly isotropic on increasing temperature at pressures of the inner core and is therefore unlikely to cause the anisotropy. An alternative explanation, supported by diamond anvil cell experiments, is that iron adopts a body- centered cubic form in the inner core. We show, by molecular dynamics simulations, that the body- centered cubic iron phase is extremely anisotropic to sound waves despite its high symmetry. Direct simulations of seismic wave propagation reveal an anisotropy of 12%, a value adequate to explain the anisotropy of the inner core.

  • 21. Belonoshko, Anatoly
    et al.
    Rosengren, Anders
    Skorodumova, Natalia
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Physics IV.
    Bastea, S
    Johansson, Börje
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Physics IV.
    Smearing of shock front in liquid deuterium at high impact velocities2005In: J.Chem.Phys., Vol. 122, p. 124503-Article in journal (Refereed)
  • 22. Belonoshko, Anatoly
    et al.
    Skorodumova, Natalia
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Physics IV.
    Rosengren, Anders
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Physics IV.
    Johansson, Börje
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Physics IV.
    Burakovsky, Leonid
    Preston, D. L.
    High-pressure melting of MgSiO32005In: Phys. Rev. Lett.,, Vol. 94, p. 195701-Article in journal (Refereed)
  • 23. Belonoshko, Anatoly
    et al.
    Skorodumova, Natalia
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Rosengren, Anders
    Johansson, Börje
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Melting and critical superheating2006In: Phys. Rev. B, Vol. 73, p. 012201-Article in journal (Refereed)
  • 24.
    Bondarenko, N.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Kvashnin, Y.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Chico, J.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Bergman, A.
    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.
    Skorodumova, N. V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Spin-polaron formation and magnetic state diagram in La-doped CaMnO32017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 95, no 22, article id 220401Article in journal (Refereed)
    Abstract [en]

    LaxCa1-xMnO3 (LCMO) has been studied in the framework of density functional theory (DFT) using Hubbard-U correction. We show that the formation of spin polarons of different configurations is possible in the G-type antiferromagnetic phase. We also show that the spin-polaron (SP) solutions are stabilized due to an interplay of magnetic and lattice effects at lower La concentrations and mostly due to the lattice contribution at larger concentrations. Our results indicate that the development of SPs is unfavorable in the C- and A-type antiferromagnetic phases. The theoretically obtained magnetic state diagram is in good agreement with previously reported experimental results.

  • 25.
    Bondarenko, Nina
    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.
    Skorodumova, Natalia V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Hole bipolaron formation at (100) MgO/CaO epitaxial interface2014In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 89, no 12, p. 125118-Article in journal (Refereed)
    Abstract [en]

    Hole localization accompanying the formation of a cation vacancy in bulk MgO and CaO and at the (100) MgO/CaO interface is described using the Heyd-Scuseria-Ernzerhof hybrid functionals and DFT + U method. The ground state is found to be the O-1-O-1 bipolaronic configuration both in bulk oxides and at their interfaces. The ground-state magnetic configuration is a triplet, which has an energy only about 1-2 meV lower than that of the singlet state. The one-centered O-2-O-0 bipolaron was found to be metastable with its stability being enhanced at the interfaces compared to that in bulk oxides. Possible transition between different biplaronic configurations at the interface are analyzed for chosen configurations.

  • 26.
    Bondarenko, Nina
    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.
    Skorodumova, Natalia. V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Royal Inst Technol, Dept Mat Sci & Engn, Multiscale Mat Modelling, SE-10044 Stockholm, Sweden..
    Polaron mobility in oxygen-deficient and lithium-doped tungsten trioxide2015In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 92, no 16, article id 165119Article in journal (Refereed)
    Abstract [en]

    Electron localization and polaron mobility in oxygen-deficient as well as Li-doped monoclinic tungsten trioxide have been studied in the adiabatic limit in the framework of density functional theory. We show that small polarons formed in the presence of oxygen vacancy prefer the bipolaronicW(5+)-W5+ configuration, whereas the W6+-W4+ configuration is found to be metastable. Our calculations suggest that bipolarons are tightly bound by the vacancy and therefore largely immobile. On the contrary, polarons formed as a result of Li intercalation can be mobile; the activation energy for polaron jumping in this case varies between 98 and 124 meV depending on the crystallographic direction. The formation of W5+-W5+ bipolarons in Li-WO3 is possible. When situated along [001] the bipolaronic configuration is 8 meV lower in energy than two separate W5+ polarons.

  • 27.
    Bondarenko, Nina G.
    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. Orebro Univ, Sch Sci & Technol, SE-70182 Orebro, Sweden.
    Skorodumova, Natalia V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Royal Inst Technol, Dept Mat Sci & Engn, Multiscale Mat Modelling, SE-10044 Stockholm, Sweden.
    Pereiro, Manuel
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Multi-polaron solutions, nonlocal effects and internal modes in a nonlinear chain2019In: Journal of physics: Condensed matter, ISSN 0953-8984, Vol. 31, no 41, article id 415401Article in journal (Refereed)
    Abstract [en]

    Multipolaron solutions were studied in the framework of the Holstein one-dimensional molecular crystal model. The study was performed in the continuous limit where the crystal model maps into the nonlinear Schrödinger equation for which a new periodic dnoidal solution was found for the multipolaron system. In addition, the stability of the multi-polaron solutions was examined, and it was found that  cnoidal and dnoidal solutions stabilize in different ranges of the parameter space. Moreover, the model was studied under the influence of nonlocal effects and the polaronic dynamics was described in terms of internal solitonic modes.

  • 28. Borman, V. D.
    et al.
    Borisyuk, P. V.
    Vasiliev, O. S.
    Pushkin, M. A.
    Tronin, V. N.
    Tronin, I. V.
    Troyan, V. I.
    Skorodumova, Natalia V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Condensed Matter Theory.
    Johansson, Börje
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Condensed Matter Theory.
    Observation of electron localization in rough gold nanoclusters on the graphite surface2007In: JETP Letters: Journal of Experimental And Theoretical Physics Letters, ISSN 0021-3640, E-ISSN 1090-6487, Vol. 86, no 6, p. 393-397Article in journal (Refereed)
    Abstract [en]

    The results of scanning tunneling spectroscopy of the electronic states of Au nanoclusters on the graphite surface are presented. The tunneling current is found to be different at different points of a rough-surface nano-cluster. The measured differential current-voltage curve of the clusters is nonmonotonic near the Fermi energy, and the tunneling conductance decreases by almost a factor of two as the cluster volume changes from I to 0.1 mm(3). This decrease can be associated with the change in the density of the electronic states near the Fermi energy. The observed features are qualitatively described within the framework of the mechanism of electron localization in disordered systems.

  • 29. Borman, V. D.
    et al.
    Johansson, Börje
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Skorodumova, Natalia
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Tronin, I. V.
    Tronin, V. N.
    Troyan, V. I.
    Diffusion and particle mobility in 1D system2006In: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 359, no 5, p. 504-508Article in journal (Refereed)
    Abstract [en]

    The transport properties of one-dimensional (1D) systems have been studied theoretically. Contradictory experimental results on molecular transport in quasi-1D systems, such as zeolite structures, when both diffusion transport acceleration and the existence of the diffusion mode with lower particle mobility (single-file diffusion (< x(2)> similar to t(1/2))) have been reported, are consolidated in a consistent model. Transition from the single-file diffusion mode to an Einstein-like diffusion < x(2)> similar to t with diffusion coefficient increasing with the density has been predicted to occur at large observation times.

  • 30. Borman, V. D.
    et al.
    Tronin, I. V.
    Tronin, V. N.
    Troyan, V. I.
    Johansson, Börje
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Condensed Matter Theory.
    Skorodumova, Natalia V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Condensed Matter Theory.
    Formation of high- and low-density clusters in a 1D system2008In: Physica. E, Low-Dimensional systems and nanostructures, ISSN 1386-9477, E-ISSN 1873-1759, Vol. 40, no 3, p. 643-648Article in journal (Refereed)
    Abstract [en]

    The properties of monoatomic chains have been studied theoretically by means of statistical mechanics methods. The applied approach can be used to evaluate the interatomic distances and lifetimes of one-dimensional (1D) and quasi-1D systems. In particular, we show that the 1D clusters of gold atoms can exist in two states with different lattice parameters (similar to 3.6 and similar to 2.8 angstrom) that can explain the whole variety of experimental observations on monoatomic gold chains without assuming any wire contamination.

  • 31.
    Chanda, Debabrata
    et al.
    Univ Chem & Technol, Dept Inorgan Technol, Tech 5, Prague 16628 6, Czech Republic.
    Dobrota, Ana S.
    Univ Belgrade, Fac Phys Chem, Studentski Trg 12-16, Belgrade 11158, Serbia.
    Hnat, Jaromir
    Univ Chem & Technol, Dept Inorgan Technol, Tech 5, Prague 16628 6, Czech Republic.
    Sofer, Zdenek
    Univ Chem & Technol, Dept Inorgan Chem, Tech 5, Prague 16628 6, Czech Republic.
    Pasti, Igor A.
    Univ Belgrade, Fac Phys Chem, Studentski Trg 12-16, Belgrade 11158, Serbia;KTH Royal Inst Technol, Dept Mat Sci & Engn, Brinellvagen 23, S-10044 Stockholm, Sweden.
    Skorodumova, Natalia V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. KTH Royal Inst Technol, Dept Mat Sci & Engn, Brinellvagen 23, S-10044 Stockholm, Sweden.
    Paidar, Martin
    Univ Chem & Technol, Dept Inorgan Technol, Tech 5, Prague 16628 6, Czech Republic.
    Bouzek, Karel
    Univ Chem & Technol, Dept Inorgan Technol, Tech 5, Prague 16628 6, Czech Republic.
    Investigation of electrocatalytic activity on a N-doped reduced graphene oxide surface for the oxygen reduction reaction in an alkaline medium2018In: International journal of hydrogen energy, ISSN 0360-3199, E-ISSN 1879-3487, Vol. 43, no 27, p. 12129-12139Article in journal (Refereed)
    Abstract [en]

    Today the search for new energy resources is a crucial topic for materials science. The development of new effective catalysts for the oxygen reduction reaction can significantly improve the performance of fuel cells as well as electrocatalytic hydrogen production. This study presents the scalable synthesis of nitrogen-doped graphene oxide for the oxygen reduction reaction. The combination of an ab initio theoretical investigation of the oxygen reduction reaction (ORR) mechanism and detailed electrochemical characterization allowed the identification of electrocatalytically active nitrogen functionalities. The dominant effect on electrocatalytic activity is the presence of graphitic and pyridinic nitrogen and also N-oxide functionalities. The overpotential of ORR for nitrogen-doped graphene oxide prepared by microwave-assisted synthesis outperformed the metal-doped graphene materials. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

  • 32. Davis, Sergio M.
    et al.
    Belonoshko, Anatoly B.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Condensed Matter Theory.
    Johansson, Börje
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Condensed Matter Theory.
    Skorodumova, Natalia V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Condensed Matter Theory.
    van Duin, Adri C. T.
    High-pressure melting curve of hydrogen2008In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 129, no 19, p. 194508-Article in journal (Refereed)
    Abstract [en]

    The melting curve of hydrogen was computed for pressures up to 200 GPa, using molecular dynamics. The inter- and intramolecular interactions were described by the reactive force field (ReaxFF) model. The model describes the pressure-volume equation of state solid hydrogen in good agreement with experiment up to pressures over 150 GPa, however the corresponding equation of state for liquid deviates considerably from density functional theory calculations. Due to this, the computed melting curve, although shares most of the known features, yields considerably lower melting temperatures compared to extrapolations of the available diamond anvil cell data. This failure of the ReaxFF model, which can reproduce many physical and chemical properties (including chemical reactions in hydrocarbons) of solid hydrogen, hints at an important change in the mechanism of interaction of hydrogen molecules in the liquid state.

  • 33.
    Delczeg-Czirjak, Erna K.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Edström, Alexander
    Werwinski, Miroslaw
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Rusz, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Skorodumova, Natalia V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Vitos, Levente
    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.
    Stabilization of the tetragonal distortion of Fe chi Co1-chi alloys by C impurities: A potential new permanent magnet2014In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 89, no 14, p. 144403-Article in journal (Refereed)
    Abstract [en]

    We have analyzed by density functional theory calculations the structural and magnetic properties of Fe-Co alloys doped by carbon. In analogy with the formation of martensite in steels we predict that such a structure also forms for Fe-Co alloys in a wide range of concentrations. These alloys are predicted to have a stable tetragonal distortion, which in turn leads to an enhanced magnetocrystalline anisotropy energy of up to 0.75 MJ/m(3) and a saturated magnetization field of 1.9 T.

  • 34.
    Diklic, Natasa P.
    et al.
    Univ Belgrade, Fac Phys Chem, Studentski Trg 12-16, Belgrade 11158, Serbia.
    Dobrota, Ana S.
    Univ Belgrade, Fac Phys Chem, Studentski Trg 12-16, Belgrade 11158, Serbia.
    Pasti, Igor A.
    Univ Belgrade, Fac Phys Chem, Studentski Trg 12-16, Belgrade 11158, Serbia;Royal Inst Technol, Sch Ind Engn & Management, Dept Mat Sci & Engn, KTH, Brinellvagen 23, S-10044 Stockholm, Sweden.
    Mentus, Slavko, V
    Univ Belgrade, Fac Phys Chem, Studentski Trg 12-16, Belgrade 11158, Serbia;Serbian Acad Arts & Sci, Knez Mihajlova 35, Belgrade 11000, Serbia.
    Johansson, Börje
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy. Royal Inst Technol, Sch Ind Engn & Management, Dept Mat Sci & Engn, KTH, Brinellvagen 23, S-10044 Stockholm, Sweden.
    Skorodumova, Natalia V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Royal Inst Technol, Sch Ind Engn & Management, Dept Mat Sci & Engn, KTH, Brinellvagen 23, S-10044 Stockholm, Sweden.
    Sodium storage via single epoxy group on graphene: The role of surface doping2019In: Electrochimica Acta, ISSN 0013-4686, E-ISSN 1873-3859, Vol. 297, p. 523-528Article in journal (Refereed)
    Abstract [en]

    Due to its unique physical and chemical properties, graphene is being considered as a promising material for energy conversion and storage applications. Introduction of functional groups and dopants on/in graphene is a useful strategy for tuning its properties. In order to fully exploit its potential, atomic-level understanding of its interaction with species of importance for such applications is required. We present a DFT study of the interaction of sodium atoms with epoxy-graphene and analyze how this interaction is affected upon doping with boron and nitrogen. We demonstrate how the dopants, combined with oxygen-containing groups alter the reactivity of graphene towards Na. Dopants act as attractors of epoxy groups, enhancing the sodium adsorption on doped oxygen-functionalized graphene when compared to the case of non-doped epoxy-graphene. Furthermore, by considering thermodynamics of the Na interaction with doped epoxy-graphene it has been concluded that such materials are good candidates for Na storage applications. Therefore, we suggest that controlled oxidation of doped carbon materials could lead to the development of advanced anode materials for rechargeable Na-ion batteries.

  • 35.
    Dobrota, Ana S.
    et al.
    Univ Belgrade, Fac Phys Chem, Studentski Trg 12-16, Belgrade 11158, Serbia..
    Gutic, Sanjin
    Fac Sci, Dept Chem, Zmaja Bosne 33-35, Sarajevo, Bosnia & Herceg..
    Kalijadis, Ana
    Univ Belgrade, Vinca Inst Nucl Sci, Mike Petrovica Alasa 12-14, Belgrade 11001, Serbia..
    Baljozovic, Milos
    Paul Scherrer Inst, Lab Micro & Nanotechnol, Villigen, Switzerland..
    Mentus, Slavko V.
    Univ Belgrade, Fac Phys Chem, Studentski Trg 12-16, Belgrade 11158, Serbia.;Serbian Acad Arts & Sci, Knez Mihajlova 35, Belgrade 11000, Serbia..
    Skorodumova, Natalia V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. KTH Royal Inst Technol, Sch Ind Engn & Management, Dept Mat Sci & Engn, Brinellvagen 23, S-10044 Stockholm, Sweden..
    Pasti, Igor A.
    Univ Belgrade, Fac Phys Chem, Studentski Trg 12-16, Belgrade 11158, Serbia..
    Stabilization of alkali metal ions interaction with OH-functionalized graphene via clustering of OH groups - implications in charge storage applications2016In: RSC Advances, ISSN 2046-2069, E-ISSN 2046-2069, Vol. 6, no 63, p. 57910-57919Article in journal (Refereed)
    Abstract [en]

    Graphene synthesized by reduction of graphene oxide, depending on the degree of reduction, retains a certain amount of surface OH groups. Considering the surface OH groups/graphene layer system by means of density functional theory calculations, we evidenced the tendency of OH groups to cluster, resulting in enhanced system stability and no band gap opening. In the oxygen concentration range between 1.8 and 8.47 at%, with the addition of each new OH group, integral binding energy decreases, while differential binding energy shows the boost at even numbers of OH groups. Furthermore, we found that the clustering of OH groups over graphene basal plane plays a crucial role in enhancing the interactions with alkali metals. Namely, if alkali metal atoms interact with individual OH groups only, the interaction leads to an irreversible formation of MOH phase. When alkali atoms interact with clusters containing odd number of OH groups, a reversible transfer of an electron charge from the metal atom to the substrate takes place without OH removal. The strength of the interaction in general increases from Li to K. In an experimental investigation of a graphene sample which dominantly contains OH groups, we have shown that the trend in the specific interaction strength reflects to gravimetric capacitances measured in alkali metal chloride solutions. We propose that the charge stored in OH groups which interact with alkali metal cation and the pi electronic system of the graphene basal plane presents the main part of its pseudocapacitance.

  • 36.
    Dobrota, Ana S.
    et al.
    Univ Belgrade, Fac Phys Chem, Studentski Trg 12-16, Belgrade 11158, Serbia..
    Pasti, Igor A.
    Univ Belgrade, Fac Phys Chem, Studentski Trg 12-16, Belgrade 11158, Serbia..
    Mentus, Slavko V.
    Univ Belgrade, Fac Phys Chem, Studentski Trg 12-16, Belgrade 11158, Serbia.;Serbian Acad Arts & Sci, Knez Mihajlova 35, Belgrade 11000, Serbia..
    Skorodumova, Natalia V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. KTH Royal Inst Technol, Dept Mat Sci & Engn, Brinellvagen 23, S-10044 Stockholm, Sweden..
    A DFT study of the interplay between dopants and oxygen functional groups over the graphene basal plane - implications in energy-related applications2017In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 19, no 12, p. 8530-8540Article in journal (Refereed)
    Abstract [en]

    Understanding the ways graphene can be functionalized is of great importance for many contemporary technologies. Using density functional theory calculations we investigate how vacancy formation and substitutional doping by B, N, P and S affect the oxidizability and reactivity of the graphene basal plane. We find that the presence of these defects enhances the reactivity of graphene. In particular, these sites act as strong attractors for OH groups, suggesting that the oxidation of graphene could start at these sites or that these sites are the most difficult to reduce. Scaling between the OH and H adsorption energies is found on both reduced and oxidized doped graphene surfaces. Using the O-2 molecule as a probe we show that a proper modelling of doped graphene materials has to take into account the presence of oxygen functional groups.

  • 37.
    Dobrota, Ana S.
    et al.
    Univ Belgrade, Fac Phys Chem, Studentski Trg 12-16, Belgrade 11158, Serbia..
    Pasti, Igor A.
    Univ Belgrade, Fac Phys Chem, Studentski Trg 12-16, Belgrade 11158, Serbia..
    Mentus, Slavko V.
    Univ Belgrade, Fac Phys Chem, Studentski Trg 12-16, Belgrade 11158, Serbia.;Serbian Acad Arts & Sci, Knez Mihajlova 35, Belgrade 11000, Serbia..
    Skorodumova, Natalia V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. KTH Royal Inst Technol, Sch Ind Engn & Management, Dept Mat Sci & Engn, Brinellvagen 23, S-10044 Stockholm, Sweden..
    A general view on the reactivity of the oxygen-functionalized graphene basal plane2016In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 18, no 9, p. 6580-6586Article in journal (Refereed)
    Abstract [en]

    In this contribution we inspect the adsorption of H, OH, Cl and Pt on oxidized graphene using DFT calculations. The introduction of epoxy and hydroxyl groups on the graphene basal plane significantly alters its chemisorption properties, which can be attributed to the deformation of the basal plane and the type and distribution of these groups. We show that a general scaling relation exists between the hydrogen binding energies and the binding energies of other investigated adsorbates, which allows for a simple probing of the reactivity of oxidized graphene with only one adsorbate. The electronic states of carbon atoms located within the 2 eV interval below the Fermi level are found to be responsible for the interaction of the basal plane with the chosen adsorbates. The number of electronic states situated in this energy interval is shown to correlate with hydrogen binding energies.

  • 38.
    Dobrota, Ana S.
    et al.
    Univ Belgrade, Fac Phys Chem, Belgrade 11158, Serbia..
    Pasti, Igor A.
    Univ Belgrade, Fac Phys Chem, Belgrade 11158, Serbia..
    Skorodumova, Natalia V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. KTH Royal Inst Technol, Sch Ind Engn & Management, Dept Mat Sci & Engn, Multiscale Mat Modelling Grp, S-10044 Stockholm, Sweden.;Uppsala Univ, Dept Phys & Astron, S-75120 Uppsala, Sweden..
    Oxidized graphene as an electrode material for rechargeable metal-ion batteries - a DFT point of view2015In: Electrochimica Acta, ISSN 0013-4686, E-ISSN 1873-3859, Vol. 176, p. 1092-1099Article in journal (Refereed)
    Abstract [en]

    In line with a growing interest in the use of graphene-based materials for energy storage applications and active research in the field of rechargeable metal-ion batteries we have performed a DFT based computational study of alkali metal atoms (Li, Na and K) interaction with an oxidized graphene. The presence of oxygen surface groups (epoxy and hydroxyl) alters the chemisorption properties of graphene. In particular, we observe that the epoxy groups are redox active and enhance the alkali metal adsorption energies by a factor of 2 or more. When an alkali metal atom interacts with hydroxyl-graphene the formation of metal-hydroxide is observed. In addition to a potential boost of metal ion storage capability, oxygen functional groups also prevent the precipitation of the metal phase. By simulating lithiation/de-lithiation process on epoxy-graphenes, it was concluded that the oxidized graphene can undergo structural changes during battery operation. Our results suggest that the content and the type of oxygen surface groups should be carefully tailored to maximize the performance of metal-ion batteries. This is mainly related to the control of the oxidation level in order to provide enough active centers for metal ion storage while preserving sufficient electrical conductivity.

  • 39.
    Fako, Edvin
    et al.
    Univ Belgrade, Fac Phys Chem, Studentski Trg 12-16, Belgrade 11158, Serbia.;Barcelona Inst Sci & Technol, ICIQ, Inst Chem Res Catalonia, Av Paisos Catalans 16, Tarragona 43007, Spain..
    Dobrota, Ana S.
    Univ Belgrade, Fac Phys Chem, Studentski Trg 12-16, Belgrade 11158, Serbia..
    Pasti, Igor A.
    Univ Belgrade, Fac Phys Chem, Studentski Trg 12-16, Belgrade 11158, Serbia.;KTH Royal Inst Technol, Sch Ind Engn & Management, Dept Mat Sci & Engn, Brinellvagen 23, S-10044 Stockholm, Sweden..
    Lopez, Nuria
    Barcelona Inst Sci & Technol, ICIQ, Inst Chem Res Catalonia, Av Paisos Catalans 16, Tarragona 43007, Spain..
    Mentus, Slavko V.
    Univ Belgrade, Fac Phys Chem, Studentski Trg 12-16, Belgrade 11158, Serbia.;Serbian Acad Arts & Sci, Knez Mihajlova 35, Belgrade 11000, Serbia..
    Skorodumova, Natalia V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Lattice mismatch as the descriptor of segregation, stability and reactivity of supported thin catalyst films2018In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 20, no 3, p. 1524-1530Article in journal (Refereed)
    Abstract [en]

    The increasing demand and high prices of advanced catalysts motivate a constant search for novel active materials with reduced contents of noble metals. The development of thin films and core-shell catalysts seems to be a promising strategy along this path. Using density functional theory we have analyzed a number of surface properties of supported bimetallic thin films with the composition A(3)B (where A = Pt and Pd, and B = Cu, Ag and Au). We focus on the surface segregation, dissolution stability and surface electronic structure. We also address the chemisorption properties of Pd3Au thin films supported by different substrates, by probing the surface reactivity with CO. We find a strong influence of the support in the case of mono- and bilayers, while the surface strain seems to be the predominant factor in determining the surface properties of supported trilayers and thicker films. In particular, we show that the studied properties of the supported trilayers can be predicted from the lattice mismatch between the overlayer and the support. Namely, if the strain dependence of the corresponding quantities for pure strained surfaces is known, the properties of strained supported trilayers can be reliably estimated. The obtained results can be used in the design of novel catalysts and predictions of the surface properties of supported ultrathin catalyst layers.

  • 40.
    Gavrilov, Nemanja
    et al.
    Univ Belgrade, Fac Phys Chem, Studentski Trg 12-16, Belgrade 11158, Serbia.
    Momcilovic, Milan
    Univ Belgrade, Inst Nucl Sci Vinca, POB 522, Belgrade 11000, Serbia.
    Dobrota, Ana S.
    Univ Belgrade, Fac Phys Chem, Studentski Trg 12-16, Belgrade 11158, Serbia.
    Stankovic, Dalibor M.
    Univ Belgrade, Inst Nucl Sci Vinca, POB 522, Belgrade 11000, Serbia;Univ Belgrade, Innovat Ctr, Fac Chem, Studentski Trg 12, Belgrade 11158, Serbia.
    Jokic, Bojan
    Univ Arts Belgrade, Fac Appl Arts, Kralja Petra 4, Belgrade 11000, Serbia;Univ Belgrade, Fac Technol & Met, Karnegijeva 4, Belgrade 11000, Serbia.
    Babic, Biljana
    Univ Belgrade, Inst Phys, Pregrev 118, Belgrade 11080, Serbia.
    Skorodumova, Natalia V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. KTH Royal Inst Technol, Dept Mat Sci & Engn, Brinellvagen 23, S-10044 Stockholm, Sweden.
    Mentus, Slavko V.
    Univ Belgrade, Fac Phys Chem, Studentski Trg 12-16, Belgrade 11158, Serbia;Serbian Acad Arts & Sci, Knez Mihajlova 35, Belgrade 11000, Serbia.
    Pasti, Igor A.
    Univ Belgrade, Fac Phys Chem, Studentski Trg 12-16, Belgrade 11158, Serbia;KTH Royal Inst Technol, Dept Mat Sci & Engn, Brinellvagen 23, S-10044 Stockholm, Sweden.
    A study of ordered mesoporous carbon doped with Co and Ni as a catalyst of oxygen reduction reaction in both alkaline and acidic media2018In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 349, p. 511-521Article in journal (Refereed)
    Abstract [en]

    The incorporation of trace amounts (< 0.2%) of Co and Ni noticeably enhanced the catalytic activity of nitrogen free ordered mesoporous carbon (OMC) towards oxygen reduction reaction (ORR). (Co,Ni)-doped OMCs were characterized by N-2-adsorption measurements, X-ray powder diffraction, field emission scanning electron microscopy and Raman spectroscopy methods, and their ORR activity was estimated by voltammetry on rotating disk electrode in acidic and alkaline media. (Co,Ni)-doped OMCs show modest activities in acidic media, while the catalytic activity in alkaline media is rather high. The measured activities are compared to the Pt-based and Pt-free ORR catalysts reported in the literature. The number of electrons consumed per O-2 in metal-doped OMCs was found to vary between 2 and 4, which is advantageous in comparison to metal-free OMC. Also, the mass activities of metal-doped OMCs were found to be up to 2.5 times higher compared to that of metal-free OMC. We suggest that the ORR activity is governed by a balance between (i) textural properties, which determine the electrochemically accessible surface of the catalyst and which are influenced by the addition of a metal precursor, and (ii) novel active sites formed upon the introduction of metals into the carbon structure. In particular, our Density Functional Theory calculations suggest that Co and Ni atoms embedded into the single vacancies of graphene can activate the O-2 molecule and contribute to the decomposition of peroxide.

  • 41.
    Grigoriev, Anton
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Skorodumova, Natalia V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Simak, S. I.
    Wendin, G.
    Johansson, Börje
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Electron transport in stretched monoatomic gold wires2006In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 97, no 23, p. 236807-Article in journal (Refereed)
    Abstract [en]

    The conductance of monoatomic gold wires containing 3-7 gold atoms has been obtained from ab initio calculations. The transmission is found to vary significantly depending on the wire stretching and the number of incorporated atoms. Such oscillations are determined by the electronic structure of the one-dimensional (1D) part of the wire between the contacts. Our results indicate that the conductivity of 1D wires can be suppressed without breaking the contact.

  • 42.
    Gutic, Sanjin J.
    et al.
    Fac Sci, Dept Chem, Zmaja & Bosne 33-35, Sarajevo 71000, Bosnia & Herceg..
    Dobrota, Ana S.
    Univ Belgrade, Fac Phys Chem, Studentski Trg 12-16, Belgrade 11158, Serbia..
    Leetmaa, Mikael
    KTH Royal Inst Technol, Dept Mat Sci & Engn, Brinellvagen 23, S-10044 Stockholm, Sweden..
    Skorodumova, Natalia. V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. KTH Royal Inst Technol, Dept Mat Sci & Engn, Brinellvagen 23, S-10044 Stockholm, Sweden.
    Mentus, Slavko V.
    Univ Belgrade, Fac Phys Chem, Studentski Trg 12-16, Belgrade 11158, Serbia.;Serbian Acad Arts & Sci, Knez Mihajlova 35, Belgrade 11000, Serbia..
    Pasti, Igor A.
    Univ Belgrade, Fac Phys Chem, Studentski Trg 12-16, Belgrade 11158, Serbia..
    Improved catalysts for hydrogen evolution reaction in alkaline solutions through the electrochemical formation of nickel-reduced graphene oxide interface2017In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 19, no 20, p. 13281-13293Article in journal (Refereed)
    Abstract [en]

    H-2 production via water electrolysis plays an important role in hydrogen economy. Hence, novel cheap electrocatalysts for the hydrogen evolution reaction ( HER) are constantly needed. Here, we describe a simple method for the preparation of composite catalysts for H-2 evolution, consisting in simultaneous reduction of the graphene oxide film, and electrochemical deposition of Ni on its surface. The obtained composites (Ni@rGO), compared to pure electrodeposited Ni, show an improved electrocatalytic activity towards HER in alkaline media. We found that the activity of the Ni@rGO catalysts depends on the surface composition ( Ni vs. C mole ratio) and on the level of structural disorder of the rGO support. We suggest that HER activity is improved via H-ads spillover from the Ni particles to the rGO support, where quick recombination to molecular hydrogen is favored. A deeper insight into such a mechanism of H-2 production was achieved by kinetic Monte-Carlo simulations. These simulations enabled the reproduction of experimentally observed trends under the assumption that the support can act as a Hads acceptor. We expect that the proposed procedure for the production of novel HER catalysts could be generalized and lead to the development of a new generation of HER catalysts by tailoring the catalyst/support interface.

  • 43. Hellman, O.
    et al.
    Skorodumova, Natalia V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Simak, S. I.
    Charge Redistribution Mechanisms of Ceria Reduction2012In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 108, no 13, p. 135504-Article in journal (Refereed)
    Abstract [en]

    Charge redistribution at low oxygen vacancy concentrations in ceria have been studied in the framework of the density functional theory. We propose a model to approach the dilute limit using the results of supercell calculations. It allows one to reproduce the characteristic experimentally observed behavior of composition versus oxygen pressure dependency. We show that in the dilute limit the charge redistribution is likely to be driven by a mechanism different from the one involving electron localization on cerium atoms. We demonstrate that it can involve charge localization on light element impurities.

  • 44.
    Huang, Lunmei
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Physics IV.
    Skorodumova, Natalia
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Physics IV.
    Belonoshko, Anatoly
    Johansson, Börje
    Ahuja, Rajeev
    Carbon in iron phases under high pressure2005In: Geophysical Research Letters, Vol. 32Article in journal (Refereed)
    Abstract [en]

    The influence of carbon impurities on the properties of iron phases (bcc, hcp, dhcp, fcc) has been studied using the first-principles projector augmented-wave (PAW) method for a wide pressure range. It is shown that the presence of ~6 at. % of interstitial carbon has a little effect on the calculated structural sequence of the iron phases under high pressure. The bcc → hcp transition both for pure iron and iron containing carbon takes place around 9 GPa. According to the enthalpies comparison, the solubility of carbon into the iron solid is decreased by high pressure. The coexistence of iron carbide (Fe3C) + pure hcp Fe is most stable phase at high pressure compared with other phases. Based on the analysis of the pressure-density dependences for Fe3C and hcp Fe, we suggest that there might be some fraction of iron carbide present in the core.

  • 45.
    Isaev, Eyvaz I.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Condensed Matter Theory.
    Skorodumova, Natalia V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Condensed Matter Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Condensed Matter Theory.
    Vekilov, Yuri K.
    Johansson, Börje
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Condensed Matter Theory.
    Dynamical stability of Fe-H in the Earth's mantle and core regions2007In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 104, no 22, p. 9168-9171Article in journal (Refereed)
    Abstract [en]

    The core extends from the depth of 2,900 km to the center of the Earth and is composed mainly of an iron-rich alloy with nickel, with 10% of the mass comprised of lighter elements like hydrogen, but the exact composition is uncertain. We present a quantum mechanical first-principles study of the dynamical stability of FeH phases and their phonon densities of states at high pressure. Our free-energy calculations reveal a phonon-driven stabilization of dhcp FeH at low pressures, thus resolving the present contradiction between experimental observations and theoretical predictions. Calculations reveal a complex phase diagram for FeH under pressure with a dhcp -> hcp -> fcc sequence of structural transitions.

  • 46.
    Jovanovic, A.
    et al.
    Univ Belgrade, Fac Phys Chem, Studentski Trg 12-16, Belgrade 11158, Serbia;CEST, Viktor Kaplan Str 2, A-2700 Wiener Neustadt, Austria.
    Dobrota, A. S.
    Univ Belgrade, Fac Phys Chem, Studentski Trg 12-16, Belgrade 11158, Serbia.
    Rafailovic, L. D.
    CEST, Viktor Kaplan Str 2, A-2700 Wiener Neustadt, Austria.
    Mentus, S. V.
    Univ Belgrade, Fac Phys Chem, Studentski Trg 12-16, Belgrade 11158, Serbia;Serbian Acad Arts & Sci, Knez Mihajlova 35, Belgrade 11000, Serbia.
    Pasti, I. A.
    Univ Belgrade, Fac Phys Chem, Studentski Trg 12-16, Belgrade 11158, Serbia;KTH Royal Inst Technol, Dept Mat Sci & Engn, Brinellvagen 23, S-10044 Stockholm, Sweden.
    Johansson, Börje
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy. KTH Royal Inst Technol, Dept Mat Sci & Engn, Brinellvagen 23, S-10044 Stockholm, Sweden;Humboldt Univ, Phys Dept, Zum Grossen Windkanal 6, D-12489 Berlin, Germany.
    Skorodumova, Natalia V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy. KTH Royal Inst Technol, Dept Mat Sci & Engn, Brinellvagen 23, S-10044 Stockholm, Sweden.
    Structural and electronic properties of V2O5 and their tuning by doping with 3d elements - modelling using the DFT plus U method and dispersion correction2018In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 20, no 20, p. 13934-13943Article in journal (Refereed)
    Abstract [en]

    New electrode materials for alkaline-ion batteries are a timely topic. Among many promising candidates, V2O5 is one of the most interesting cathode materials. While having very high theoretical capacity, in practice, its performance is hindered by its low stability and poor conductivity. As regards the theoretical descriptions of V2O5, common DFT-GGA calculations fail to reproduce both the electronic and crystal structures. While the band gap is underestimated, the interlayer spacing is overestimated as weak dispersion interactions are not properly described within GGA. Here we show that the combination of the DFT+U method and semi-empirical D2 correction can compensate for the drawbacks of the GGA when it comes to the modelling of V2O5. When compared to common PBE calculations, with a modest increase in the computational cost, PBE+U+D2 fully reproduced the experimental band gap of V2O5, while the errors in the lattice parameters are only a few percent. Using the proposed PBE+U+D2 methodology we studied the doping of V2O5 with 3d elements (from Sc to Zn). We show that both the structural and electronic parameters are affected by doping. Most importantly, a significant increase in conductivity is expected upon doping, which is of great importance for the application of V2O5 in metal-ion batteries.

  • 47.
    Jovanovic, Aleksandar
    et al.
    Univ Belgrade, Fac Phys Chem, Studentski Trg 12-16, Belgrade 11158, Serbia;Oberflachentechnol GmbH, CEST Kompetenzzentrum Elektrochem, Viktor Kaplan Str 2,Sect A, A-2700 Wiener Neustadt, Austria.
    Petkovic, Milena
    Univ Belgrade, Fac Phys Chem, Studentski Trg 12-16, Belgrade 11158, Serbia.
    Pasti, Igor A.
    Univ Belgrade, Fac Phys Chem, Studentski Trg 12-16, Belgrade 11158, Serbia;KTH Royal Inst Technol, Sch Ind Engn & Management, Dept Mat Sci & Engn, Brinellvagen 23, S-10044 Stockholm, Sweden.
    Johansson, Börje
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. KTH Royal Inst Technol, Sch Ind Engn & Managment, Dept Mat Sci & Engn, Brinellvagen 23, S-10044 Stockholm, Sweden;Humboldt Univ, Phys Dept, Zum Grossen Windkanal 6, D-12489 Berlin, Germany.
    Skorodumova, Natalia V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. KTH Royal Inst Technol, Sch Ind Engn & Management, Dept Mat Sci & Engn, Brinellvagen 23, S-10044 Stockholm, Sweden.
    Tuning the electronic and chemisorption properties of hexagonal MgO nanotubes by doping: Theoretical study2018In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 457, p. 1158-1166Article in journal (Refereed)
    Abstract [en]

    Oxide materials offer a wide range of interesting physical and chemical properties. Even more versatile behavior of oxides is seen at the nanoscale, qualifying these materials for a number of applications. In this study we used DFT calculations to investigate the physical and chemical properties of small hexagonal MgO nanotubes of different length. We analyzed the effect of Li, B, C, N, and F doping on the properties of the nanotubes. We find that all dopants favor the edge positions when incorporated into the nanotubes. Doping results in the net magnetization whose value depends on the type of the impurity. Using the CO molecule as a probe, we studied the adsorption properties of pristine and doped MgO nanotubes. Our results show that the dopant sites are also the centers of significantly altered chemical reactivity. While pristine MgO nanotubes adsorb CO weakly, very strong adsorption at the dopant sites (B-, C-, and N-doped nanotubes) or neighboring edge atoms (F- and Li-doped nanotubes) is observed. Our results suggest that impurity engineering in oxide materials can be a promising strategy for the development of novel materials with possible use as selective adsorbents or catalysts.

  • 48. Kantor, I
    et al.
    Dubrovinsky, L
    McCammon, C
    Steinle-Neumann, G
    Kantor, A
    Skorodumova, Natalia V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Pascarelli, S
    Aquilanti, G
    Short-range order and Fe clustering in Mg1-xFexO under high pressure2009In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 80, no 1, p. 014204-Article in journal (Refereed)
    Abstract [en]

    By combining high-pressure and high-temperature Moumlssbauer spectroscopic studies of (Mg,Fe)O with results of ab initio simulations, several important properties of this material were established. Under high pressure (Mg,Fe)O shows changes in the short-range order with the tendency to form iron clusters. These changes were found to be irreversible, implying sluggish kinetics of these processes at ambient conditions. The pressure-induced spin crossover is interpreted here as a gradual noncooperative transition. The onset and width of spin crossover depends, therefore, not only on pressure, temperature, and composition, but also on short-range order in the FeO-MgO solid solution.

  • 49.
    Karacic, Dalibor
    et al.
    Univ Belgrade, Fac Phys Chem, Studentski Trg 12-16, Belgrade 11158, Serbia.
    Korac, Selma
    Univ Sarajevo, Fac Sci, Dept Chem, Zmaja Bosne 33-35, Sarajevo 71000, Bosnia & Herceg.
    Dobrota, Ana S.
    Univ Belgrade, Fac Phys Chem, Studentski Trg 12-16, Belgrade 11158, Serbia.
    Pasti, Igor A.
    Univ Belgrade, Fac Phys Chem, Studentski Trg 12-16, Belgrade 11158, Serbia;KTH Royal Inst Technol, Dept Mat Sci & Engn, Sch Ind Engn & Management, Brinellvagen 23, S-10044 Stockholm, Sweden.
    Skorodumova, Natalia V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy. KTH Royal Inst Technol, Dept Mat Sci & Engn, Sch Ind Engn & Management, Brinellvagen 23, S-10044 Stockholm, Sweden.
    Gutic, Sanjin J.
    Univ Sarajevo, Fac Sci, Dept Chem, Zmaja Bosne 33-35, Sarajevo 71000, Bosnia & Herceg.
    When supporting electrolyte matters: Tuning capacitive response of graphene oxide via electrochemical reduction in alkali and alkaline earth metal chlorides2019In: Electrochimica Acta, ISSN 0013-4686, E-ISSN 1873-3859, Vol. 297, p. 112-117Article in journal (Refereed)
    Abstract [en]

    The ability to tune charge storage properties of graphene oxide (GO) is of utmost importance for energy conversion applications. Here we show that the electrochemical reduction of GO is highly sensitive to the cations present in the solution. GO is reduced at more negative potential in alkali metal chloride solutions than in alkaline earth metal chlorides. During the reduction, the capacitance of GO increases from 10 to 70 times. The maximum capacitances of reduced GO are between 65 and 130 F g-1, depending on the electrolyte and the presence of conductive additive. We propose that different interactions of cations with oxygen functional groups of GO during the reduction are responsible for the observed effect. This hypothesis has been confirmed by Density Functional Theory calculations of alkali and alkaline earth metals interactions with epoxy-functionalized graphene sheet.

  • 50.
    Klarbring, Johan
    et al.
    Linköping Univ, Dept Phys Chem & Biol IFM, SE-58183 Linkoping, Sweden..
    Skorodumova, Natalia V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. KTH Royal Inst Technol, Mat Sci & Engn Dept, Stockholm, Sweden..
    Simak, Sergei I.
    Linköping Univ, Dept Phys Chem & Biol IFM, SE-58183 Linkoping, Sweden..
    Finite-temperature lattice dynamics and superionic transition in ceria from first principles2018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, no 10, article id 104309Article in journal (Refereed)
    Abstract [en]

    Ab initio molecular dynamics (AIMD) in combination with the temperature dependent effective potential (TDEP) method has been used to go beyond the quasiharmonic approximation and study the lattice dynamics in ceria, CeO2, at finite temperature. The results indicate that the previously proposed connection between the B-1u phonon mode turning imaginary and the transition to the superionic phase in fluorite structured materials is an artifact of the failure of the quasiharmonic approximation in describing the lattice dynamics at elevated temperatures. We instead show that, in the TDEP picture, a phonon mode coupling to the E-u mode prevents the B-1u mode from becoming imaginary. We directly observe the superionic transition at high temperatures in our AIMD simulations and find that it is initiated by the formation of oxygen Frenkel pairs (FP). These FP are found to form in a collective process involving simultaneous motion of two oxygen ions.

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