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  • 1. Airiskallio, E.
    et al.
    Nurmi, E.
    Vayrynen, I. J.
    Kokko, K.
    Ropo, M.
    Punkkinen, M. P. J.
    Johansson, Bengt
    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.
    Magnetic origin of the chemical balance in alloyed Fe-Cr stainless steels: First-principles and Ising model study2014In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 92, p. 135-140Article in journal (Refereed)
    Abstract [en]

    Iron-chromium is the base material for most of the stainless steel grades. Recently, new insights into the origins of fundamental physical and chemical characteristics of Fe-Cr based alloys have been achieved. Some of the new results are quite unexpected and call for further investigations. The present study focuses on the magnetic contribution in the atomic driving forces related to the chemical composition in Fe-Cr when alloyed with Al, Ti, V, Mn, Co, Ni, and Mo. Using the ab initio exact muffin-tin orbitals method combined with an Ising-type spin model, we demonstrate that the magnetic moment of the solute atoms with the induced changes in the magnetic moments of the host atoms form the main factor in determining the mixing energy and chemical potentials of low-Cr Fe-Cr based alloys. The results obtained in the present work are related to the designing and tuning of the microstructure and corrosion protection of low-Cr steels. (C) 2014 Elsevier B. V. All rights reserved.

  • 2. Al-Zoubi, N.
    et al.
    Punkkinen, M. P. J.
    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.
    Influence of magnesium on hydrogenated ScAl(1-x)Mg(x) alloys: A theoretical study2011In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 50, no 10, p. 2848-2853Article in journal (Refereed)
    Abstract [en]

    Ab initio total energy calculations, based on the projector augmented wave method and the exact muffin-tin orbitals method in combination with the coherent-potential approximation, are used to examine the effect of magnesium on hydrogen absorption/desorption temperature and phase stability of hydrogenated ScAl(1-x)Mg(x) (0 <= x <= 0.3) alloys. According to the experiments, ScAl(1-x)Mg(x) adopts the CsCl structure, and upon hydrogen absorption it decomposes into ScH(2) with CaF(2) structure and Al-Mg with face centered cubic structure. Here we demonstrate that the stability field of the hydrogenated alloys depends sensitively on Mg content and on the microstructure of the decomposed system. For a given microstructure, the critical temperature for hydrogen absorption/desorption increases with Mg concentration.

  • 3.
    Al-Zoubi, Noura
    et al.
    Tafila Tech Univ, Dept Appl Phys, Tafila, Jordan.
    Schonecker, Stephan
    KTH Royal Inst Technol, Dept Mat Sci & Engn, Appl Mat Phys, SE-10044 Stockholm, Sweden.
    Li, Xiaoqing
    KTH Royal Inst Technol, Dept Mat Sci & Engn, Appl Mat Phys, SE-10044 Stockholm, Sweden.
    Li, Wei
    KTH Royal Inst Technol, Dept Mat Sci & Engn, Appl Mat Phys, SE-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, Dept Mat Sci & Engn, Appl Mat Phys, SE-10044 Stockholm, Sweden.
    Vitos, Levente
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. KTH Royal Inst Technol, Dept Mat Sci & Engn, Appl Mat Phys, SE-10044 Stockholm, Sweden; Wigner Res Ctr Phys, Res Inst Solid State Phys & Opt, POB 49, H-1525 Budapest, Hungary.
    Elastic properties of 4d transition metal alloys: Values and trends2019In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 159, p. 273-280Article in journal (Refereed)
    Abstract [en]

    Using the Exact Muffin-Tin Orbitals method within the Perdew-Burke-Ernzerhof exchange-correlation approximation for solids and solid surfaces (PBEso1), we study the single crystal elastic constants of 4d transition metals (atomic number Z between 39 and 47) and their binary alloys in the body centered cubic (bcc) and face centered cubic (fcc) structures. Alloys between the first neighbors Z(Z + 1) and between the second neighbors Z(Z + 2) are considered. The lattice constants, bulk moduli and elastic constants are found in good agreement with the available experimental and theoretical data. It is shown that the correlation between the relative tetragonal shear elastic constant C-fcc'-2C(bcc)' and the structural energy difference between the fcc and bcc lattices Delta E is superior to the previously considered models. For a given crystal structure, the equiatomic Z(Z + 2) alloys turn out to have similar structural and elastic properties as the pure elements with atomic number (Z + 1). Furthermore, alloys with composition Z(1-x)(Z + 2)(x) possess similar properties as Z(1-2x)(Z + 1)(2x). The present theoretical data on the structural and the elastic properties of 4d transition metal alloys provides consistent input for coarse scale modeling of material properties.

  • 4.
    Edin, Emil
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Luo, Wei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Kaplan, Bartek
    Sandvik Coromant R&D, Stockholm, Sweden.
    Blomqvist, Andreas
    Sandvik Coromant R&D, Stockholm, Sweden.
    First principles study of C diffusion in WC/W interfaces observed in WC/Co tools after Ti-alloy machining2019In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 161, p. 236-243Article in journal (Refereed)
    Abstract [en]

    Ti-alloys have many qualities making them ideal for use in aerospace applications, medical implants and chemical industries such as high strength to weight ratio, good high temperature strength and chemical stability. One downside to Ti-alloys is, however, that they are considered difficult to machine. Several investigations have been made in order to understand the wear mechanisms present in machining of Ti-alloys and the most common understanding is a combination of attrition and dissolution-diffusion. Observations by Odelros et al. [1] have shown that there exists a small layer of pure bcc W on top of the outermost WC grains after turning of Ti-6Al-4V. In order for such a layer to form C has to diffuse away from the WC leaving behind only W. In this work Density Functional Theory (DFT) is used together with Harmonic Transition State Theory (HTST) to investigate the prefactors and barriers for C diffusion into and within two different WC/W interfaces, [0001]/[111] and [10 (1) over bar0]/[100]. The diffusion into the interfaces show that the barrier for the [0001]/[111] interface is more than twice as high as the barrier for the [10 (1) over bar0]/[100] interface. Diffusion within the interfaces show, on average, slightly higher barriers for the [0001]/[111] interface.

  • 5.
    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.

  • 6.
    Kaewmaraya, Thanayut
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    De Sarkar, Abir
    Sa, Baisheng
    Sun, Z.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Strain-induced tunability of optical and photocatalytic properties of ZnO mono-layer nanosheet2014In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 91, p. 38-42Article in journal (Refereed)
    Abstract [en]

    Strain-induced tunability of several properties of ZnO monolayer nanosheet has been systematically studied using density functional theory. The band gap of the sheet varies almost linearly with uniaxial strain, while it shows a parabola-like behavior under homogeneous biaxial strain. Tensile strain reduces ionicity of Zn-O bonds, while compressive strain increases it. This provides ample implications for the photocatalytic dissociation of water molecules and the scission of polar molecules on ZnO nanosheet. The dynamical stability of the sheet assessed by the calculation of its vibrational frequencies has shown the sheet to be unstable for 10% and 7.5% compressive biaxial homogeneous strain. 

  • 7.
    Kaewmaraya, Thanayut
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ramzan, Muhammad
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Sun, W.
    Sagynbaeva, Myskal
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Applied Materials Physics, Department of Materials and Engineering, Royal Institute of Technology (KTH), SE-100 44 Stockholm, Sweden.
    Atomistic study of promising catalyst and electrode material for memory capacitors: Platinum Oxides2013In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 79, p. 804-810Article in journal (Refereed)
    Abstract [en]

    Platinum oxides have the technological importance as evidenced by numerous studies concentrating on their crystal structures to attain the clear atomistic understanding but the controversy exists between the experimental and theoretical studies. In our present study, we report the electronic and optical properties of crystalline PtO and PtO2 on the basis of Heyd-Scuseria-Ernzerhof (HSE06) functional within the framework of the density functional theory (DFT). We present the structural parameters, electronic and optical properties of several proposed structures of PtO and PtO2. We find that PtS-type structure of PtO and CaCl2-type structure of PtO2 are the most stable structures of these materials on the basis of hybrid functional and they appear to be semiconductors with band gap values of 0.87 eV and 1.85 eV, respectively. The mechanical stability of these structures is also confirmed by calculating the phonon band structures. The corresponding structural parameters are found in good agreement with experimental values. Furthermore, we present the bader charge analysis and optical properties of these phases. 

  • 8. Karlström, Gunnar
    et al.
    Lindh, Roland
    Department of Theoretical Chemistry, Lund University.
    Malmqvist, Per-Åke
    Roos, Björn O
    Ryde, Ulf
    Veryazov, Valera
    Widmark, Per-Olof
    Cossi, Maurizio
    Schimmelpfennig, Bernd
    Neogrady, Pavel
    Seijo, Luis
    MOLCAS: a program package for computational chemistry2003In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 28, no 2, p. 222-239Article in journal (Refereed)
    Abstract [en]

    The program system MOLCAS is a package for calculations of electronic and structural properties of molecular systems in gas, liquid, or solid phase. It contains a number of modern quantum chemical methods for studies of the electronic structure in ground and excited electronic states. A macromolecular environment can be modeled by a combination of quantum chemistry and molecular mechanics. It is further possible to describe a crystalline material using model potentials. Solvent effects can be treated using continuum models or by combining quantum chemical calculations with molecular dynamics or Monte-Carlo simulations. MOLCAS is especially adapted to treat systems with a complex electronic structure, where the simplest quantum chemical models do not work. These features together with the inclusion of relativistic effects makes it possible to treat with good accuracy systems including atoms from the entire periodic system. MOLCAS has effective methods for geometry optimization of equilibria, transition states, conical intersections, etc. This facilitates studies of excited state energy surfaces, spectroscopy, and photochemical processes.

  • 9. Kissavos, A. E.
    et al.
    Simak, S. I.
    Olsson, Pär
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Neutron Research.
    Vitos, Levente
    Abrikosov, Igor A.
    Total energy calculations for systems with magnetic and chemical disorder2006In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 35, no 1, p. 1-5Article in journal (Refereed)
    Abstract [en]

    The accuracy of the exact muffin-tin orbitals method combined with the coherent potential approximation (EMTO-CPA) for totalenergycalculations for systems with magnetic and chemicaldisorder, which is present simultaneously, is investigated. The mixing enthalpy of ordered, as well as disordered FeCo, FeNi, and FeCu equiatomic ferromagnetic alloys is calculated with the EMTO-CPA method and with the full-potential projector augmented wave (PAW) method. The results are compared and found to be in excellent agreement with each other. The EMTO-CPA method, in combination with disordered local moment model, is then applied to calculate the mixing enthalpy of the random paramagnetic face-centered cubic (fcc) FeCo alloy, as well as body-centered cubic (bcc) FeCr and FeV alloys over the whole concentration range. The results are compared with experimental data and a very good agreement is found again.

  • 10.
    Klintenberg, Mattias
    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.
    Possible high-temperature superconductors predicted from electronic structure and data-filtering algorithms2013In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 67, p. 282-286Article in journal (Refereed)
    Abstract [en]

    We report here the completion of the electronic structure of the majority of the known stoichiometric inorganic compounds, as listed in the Inorganic Crystal Structure Data-base (ICSD). We make a detailed comparison of the electronic structure, crystal geometry and chemical bonding of cuprate high temperature superconductors, with the calculated over 60,000 electronic structures. Based on compelling similarities of the electronic structures in the normal state and a data-filtering technique, we propose that high temperature superconductivity is possible for electron-or hole-doping in a much larger group of materials than previously considered. The identified materials are composed of over 100 layered compounds, most which hitherto are untested with respect to their super conducting properties. Of particular interest are the following materials; Ca2CuBr2O2, K2CoF4, and Sr2MoO4, which are discussed in detail.

  • 11.
    Koči, L.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Condensed Matter Theory.
    Ahuja, R.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Belonoshko, A. B.
    The impact of system restriction in molecular dynamics applied to the melting of Ne at high pressure2008In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 44, no 2, p. 605-610Article in journal (Refereed)
    Abstract [en]

    There are two major ways to perform molecular dynamics (MD) calculations, namely classical and ab initio MD. As ab initio techniques require considerably longer calculation times, it is of interest to compare the results of the two methods. Furthermore, when melting is studied with MD, the use of coexistent solid and liquid structures (two-phase) in the calculations, instead of only a solid structure (one-phase), can have a substantial impact on the results   obtained. In this work, comparisons have been made between classical and ab initio methods applied to one- and two-phase systems for the melting of Ne at high pressure. The temperatures needed to melt the classical one-phase system are somewhat higher compared to the two-phase temperatures, evaluated at the same pressure. Furthermore,   there is a significant discrepancy comparing the one-phase ab initio curve to previously reported classical predictions. At 150 GPa, the calculations in this work show a melting temperature approximately 1000 K above the estimate based on an exponential-6 potential. However, there is a close match between the one-phase ab initio curve and the classical one-phase results in this work. This suggests a possible agreement between a two-phase ab initio and classical two-phase melting curve.

  • 12.
    Larsson, Peter
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Liivat, Anti
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry, Structural Chemistry.
    Thomas, John O.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry, Structural Chemistry.
    Structural and electrochemical aspects of Mn substitution into Li2FeSiO4 from DFT calculations2010In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 47, no 3, p. 678-684Article in journal (Refereed)
    Abstract [en]

    DFT calculations are presented which probe the effect of low-concentration Mn substitution of the Fe-sites in Li2FeSiO4: the promising new and potentially cheap cathode material for upscaled Li-ion battery applications. The LixFe0.875Mn0.125SiO4 System investigated could be achieved by replacing 12.5% of the Fe-sites in 2 x 2 x 1 and 2 x 2 x 2 supercells by Mn ions. The evolution of Bader charges and partial densities of states (DOS) have been followed under a stepwise delithiation process. A clear structural distortion is seen to occur at the Mn-site on delithiation, suggesting possible structural instability. Oxidation of Mn beyond 3+ is calculated to occur at potentials in excess of 4.7 V, implying that oxidation of well separated (>10 angstrom) low-concentration Mn ions to Mn4+ is energetically unfavourable in the LixFe0.875Mn0.125SiO4 structure. This, together with previous DFT results for higher levels of Mn substitution into Li2FeSiO4, indicates that capacity increase in Li2Fe1 (-) yMnySiO4 through a > 1 electron redox reaction may not be so readily attainable in practice, either for high or low Mn concentrations.

  • 13.
    Lebègue, Sébastien
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Arnaud, B.
    Alouani, M.
    Molecular dynamics simulation and chemical bonding analysis of MgB2C22006In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 37, no 3, p. 220-225Article in journal (Refereed)
    Abstract [en]

    The possible superconducting material MgB2C2 is studied by means of the Projector Augmented Plane wave method. The experimental lattice parameters and internal coordinates are reproduced with accuracy by means of a molecular dynamics calculation. A chemical bonding analysis is performed and it is found that the charge transfer from the Mg atoms to the BC network is not complete, meaning that a significant part of covalent bonding is present in this bond. In addition, a crystal orbital overlap population calculation reveals the degree of covalent bonding between atoms. This analysis is of particular importance and helps improve our general understanding of the superconductivity in these type of materials.

  • 14.
    Levamaki, H.
    et al.
    Royal Inst Technol, Appl Mat Phys, Dept Mat Sci & Engn, SE-10044 Stockholm, Sweden.
    Tian, L-Y
    Royal Inst Technol, Appl Mat Phys, Dept Mat Sci & Engn, SE-10044 Stockholm, Sweden.
    Vitos, Levente
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Royal Inst Technol, Appl Mat Phys, Dept Mat Sci & Engn, SE-10044 Stockholm, Sweden;Hungarian Acad Sci, Wigner Res Ctr Phys, Inst Solid State Phys & Opt, POB 49, H-1525 Budapest, Hungary.
    Ropo, M.
    Univ Turku, Dept Phys & Astron, FI-20014 Turku, Finland;Tampere Univ Technol, Dept Phys, FI-33101 Tampere, Finland.
    An automated algorithm for reliable equation of state fitting of magnetic systems2019In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 156, p. 121-128Article in journal (Refereed)
    Abstract [en]

    In computational physics and materials science ground-state properties are often extracted from an equation of state fit to energy-volume data. Magnetic systems often have multiple magnetic phases present in the energy-volume data, which poses a challenge for the fitting approach because the results are sensitive to the selection of included fitting points. This is because practically all popular equation of state fitting functions, such as Murnaghan and Birch-Murnaghan, assume just one phase and therefore cannot correctly fit magnetic energy-volume data that contains multiple phases. When fitting magnetic energy-volume data it is therefore important to select the range of fitting points in such a way that only points from the one relevant phase are included. We present a simple algorithm that makes the point selection automatically. Selecting fitting points automatically removes human bias and should also be useful for large-scale projects where selecting all fitting points by hand is not feasible.

  • 15.
    Li, Ruihuan
    et al.
    Dalian Univ Technol, Key Lab Mat Modificat Laser Ion & Electron Beams, Minist Educ, Dalian 116024, Peoples R China.;Royal Inst Technol, Dept Mat Sci & Engn, Appl Mat Phys, SE-10044 Stockholm, Sweden..
    Zhang, Pengbo
    Dalian Univ Technol, Key Lab Mat Modificat Laser Ion & Electron Beams, Minist Educ, Dalian 116024, Peoples R China.;Dalian Maritime Univ, Dept Phys, Dalian 116026, Peoples R China..
    Li, Xiaojie
    Dalian Univ Technol, Key Lab Mat Modificat Laser Ion & Electron Beams, Minist Educ, Dalian 116024, Peoples R China..
    Ding, Jianhua
    Dalian Univ Technol, Key Lab Mat Modificat Laser Ion & Electron Beams, Minist Educ, Dalian 116024, Peoples R China..
    Wang, Yuanyuan
    Dalian Univ Technol, Key Lab Mat Modificat Laser Ion & Electron Beams, Minist Educ, Dalian 116024, Peoples R China..
    Zhao, Jijun
    Dalian Univ Technol, Key Lab Mat Modificat Laser Ion & Electron Beams, Minist Educ, Dalian 116024, Peoples R China..
    Vitos, Levente
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Royal Inst Technol, Dept Mat Sci & Engn, Appl Mat Phys, SE-10044 Stockholm, Sweden..
    Effects of Cr and W additions on the stability and migration of He in bcc Fe: A first-principles study2016In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 123, p. 85-92Article in journal (Refereed)
    Abstract [en]

    Density functional theory calculations have been performed to study the effects of alloying Cr and W on the stability and diffusivity of interstitial He impurity in body-centered cubic (bcc) Fe host lattice. The interaction between two close Cr/W atoms is repulsive. The relative stable position for an interstitial He remains the tetrahedral interstitial site in the presence Cr. Energetically, He prefers to locate far away from W inside Fe host lattice due to the strong repulsive interaction between He and W. On the other hand, the He migration barrier becomes lower in the presence of Cr (0.026 eV) and W(0.049 eV), as compared to 0.059 eV for pure Fe. Addition of Cr is benefit for He self-trapping, while W is against. The effective diffusivity of He decreases with increasing Cr and W concentrations. Moreover, the additions of Cr and W slightly hinder He being trapped by monovacancy.

  • 16. Li, Wei
    et al.
    Lu, Song
    Hu, Qing-Miao
    Mao, Huahai
    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.
    The effect of Al on the 475 degrees C embrittlement of Fe-Cr alloys2013In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 74, p. 101-106Article in journal (Refereed)
    Abstract [en]

    Aluminum addition to ferritic stainless steels was found to effectively suppress the deleterious 475 degrees C embrittlement resulting from the phase decomposition in concentrated Fe-Cr alloys. With the aim of revealing the mechanism behind this prosperous phenomenon, here we investigate the effect of Al on the interfacial energy and formation energy of Fe-Cr solid solutions. The interface between the decomposed Fe-rich alpha and Cr-rich alpha' phases carries a positive excess energy, which is of significant importance on determining the process of phase separation. Using ab initio alloy theory, we show that for the alpha-Fe70Cr20Al10/alpha'-Fe100-x-yCryAlx (0 <= x <= 10, 55 <= y <= 80) interface, the Al content (x) barely changes the interfacial energy. However, for the alpha-Fe100-x-yCryAlx/alpha'-Fe10Cr90 (0 <= x <= 10, 0 <= y <= 25) interface, the interfacial energy increases with Al content due to the variation of the formation energies of the Fe-Cr alloys upon Al alloying. Our ab initio results are supported by CALPHAD calculations, and suggest that the beneficial effect of Al on ferritic steels is mainly due to its thermodynamical effect on the alpha' phase. 

  • 17.
    Li, Yunguo
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Li, Yan-Ling
    Sun, Weiwei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Dynamic stability of the single-layer transition metal dichalcogenides2014In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 92, p. 206-212Article in journal (Refereed)
    Abstract [en]

    In the quest for advanced semi-conductors, we have expanded our knowledge on a series of single-layer TMDs by calculating the electronic structure and lattice dynamic stability based on the first-principles density functional theory. The single layers of Mo and W dichalcogenides are found to be stable with P-6m2 symmetry. The reduction of dimension opens up and increases the bandgap. The charge transfer is found to decrease from sulfide to selenide and to telluride due to the decrease of electronegativity of chalcogen, which also induces the reduction of bandgap. The TA mode softening is found along Gamma-K direction and becomes more significant from sulfide to selenide and to telluride in the single-layer TMDs of Mo and W, which corresponds to the vibration of transition metal cations along y-axis. The single layers of Nb dichalcogenides are found to be instable with P-6m2 symmetry but stable with P-3m1 symmetry. It is also speculated that the interactions of cations mediated by electron-phonon coupling are accountable for the dynamic instability of the single-layer TMDs of Nb with P-6m2 symmetry. The unstable P-6m2 single-layer Nb dichalcogenides can transform to the stable P-3m1 structure during the exfoliation from the bulk, via the displacement of two anion layers of the sandwich structure.

  • 18.
    Liivat, Anti
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry, Structural Chemistry.
    Thomas, John O.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry.
    A DFT study of VO43- polyanion substitution into the Li-ion battery cathode material Li2FeSiO42010In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 50, no 1, p. 191-197Article in journal (Refereed)
    Abstract [en]

    Density Functional Theory (DFT) has here been used to study the substitution of SiO44- for VO43- polyanions in the orthosilicate Li-ion battery cathode material Li2FeSiO4, in order to enhance electron transfer between the TM-ions and thereby achieve a capacity increase from the potential redox activity of the orthovanadate polyanion. Comparison of results for five different model structures for LiFeXO4, X = Si, P and V, reveals that VO43- substitution destabilizes the tetrahedral structures towards olivine- or spinel-type structures. Our modelling of lithiation of the hypothetical 100% substituted system LiFeVO4 to Li2FeVO4 predicts the reduction of V5+ in the VO43- anion to V4+ at a potential of 2.1 V. While complete delithiation of LiFeVO4 to FeVO4 is accompanied by Fe2+/Fe3+ oxidation at similar to 3.1 V. These lithiation and delithiation processes trigger changes in the unit-cell volume: -6% and +10%, respectively. Notably, only minor structural distortions were observed in both VO43- and the more exotic VO44- tetrahedra. Thermodynamically feasible VO43- substitution levels are also shown to be <30%. This is exemplified for a 12.5% VO4-substituted system which exhibits similar to 50% smaller band-gap and increased capacity at an average deintercalation potential of similar to 3.2 V compared to the un-substituted system.

  • 19.
    Liu, Peng
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    De Sarkar, Abir
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Shear strain induced indirect to direct transition in band gap in AlN monolayer nanosheet2014In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 86, p. 206-210Article in journal (Refereed)
    Abstract [en]

    The electronic band structure of aluminum nitride (AlN) nanosheets under different kinds of strains has been investigated. Our first principles based studies show that the homogeneous biaxial strain is most effective as compared to uniaxial and shear strain in tuning the band gap. Large shear strain (>= 7.5%) and 10% uniaxial strain along the zig-zag direction induces an indirect-to-direct transition in band gap. The response of these 2 dimensional AlN nanosheets to strain is different from that of its 3 dimensional bulk phase counterparts to pressure. Quantum confinement effects govern the behavior of the former. The dynamical stability of AlN nanosheets have also been assessed under different modes of strains through phonon dispersion calculations. The AlN nanosheets are found to be dynamically stable under tensile strain and shear strain along zig-zag directions, while the sheets are found to be unstable under compressive strain.

  • 20. Lu, Song
    et al.
    Hu, Qing-Miao
    Yang, Rui
    Johansson, Börje
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Vitos, Levente
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Rare earth elements in alpha-Ti: A first-principles investigation2009In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 46, no 4, p. 1187-1191Article in journal (Refereed)
    Abstract [en]

    The interaction energies between substitutional rare earth (RE) atoms, between RE and interstitial C, N, O, H atoms, as well as between RE and vacancies in alpha-Ti are calculated via first-principles density-functional theory with projector augmented-wave (PAW) pseudopotentials. The results show that the RE-vacancy and RE-RE interactions are attractive due to the weaker RE-Ti bond than the host Ti-Ti bond. All of the RE atoms investigated in this paper are repulsive to C and N, but attractive to H. RE-O interactions are repulsive for the light RE atoms, though the interactions are very weak for the heavy RE atoms. The mechanism underlying the interactions and their possible influence on the properties of Ti alloys are discussed. (C) 2009 Elsevier B.V. All rights reserved.

  • 21.
    Nieves, P.
    et al.
    Univ Burgos, Int Res Ctr Crit Raw Mat & Adv Ind Technol, ICCRAM, Burgos 09001, Spain.
    Arapan, S.
    Univ Burgos, Int Res Ctr Crit Raw Mat & Adv Ind Technol, ICCRAM, Burgos 09001, Spain;VSB Tech Univ Ostrava, IT4Innovat, 17 Listopadu 15, CZ-70833 Ostrava, Czech Republic.
    Maudes-Raedo, J.
    Univ Burgos, Dept Civil Engn, Burgos 09006, Spain.
    Marticorena-Sanchez, R.
    Univ Burgos, Dept Civil Engn, Burgos 09006, Spain.
    Del Brio, N. L.
    Univ Burgos, Int Res Ctr Crit Raw Mat & Adv Ind Technol, ICCRAM, Burgos 09001, Spain.
    Kovacs, A.
    Danube Univ Krems, Dept Integrated Sensor Syst, A-3500 Krems, Austria.
    Echevarria-Bonet, C.
    Basque Ctr Mat Applicat & Nanostruct, BCMat, UPV EHU Sci Pk, Leioa 48940, Spain.
    Salazar, D.
    Basque Ctr Mat Applicat & Nanostruct, BCMat, UPV EHU Sci Pk, Leioa 48940, Spain.
    Weischenberg, J.
    Tech Univ Darmstadt, Dept Mat & Geosci, D-64287 Darmstadt, Germany.
    Zhang, H.
    Tech Univ Darmstadt, Dept Mat & Geosci, D-64287 Darmstadt, Germany.
    Vekilova, Olga Yu.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Serrano-Lopez, R.
    Univ Burgos, Int Res Ctr Crit Raw Mat & Adv Ind Technol, ICCRAM, Burgos 09001, Spain.
    Barandiaran, J. M.
    Basque Ctr Mat Applicat & Nanostruct, BCMat, UPV EHU Sci Pk, Leioa 48940, Spain.
    Skokov, K.
    Tech Univ Darmstadt, Dept Mat & Geosci, D-64287 Darmstadt, Germany.
    Gutfleisch, O.
    Tech Univ Darmstadt, Dept Mat & Geosci, D-64287 Darmstadt, Germany.
    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 Orebro, Sweden.
    Herper, Heike C.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Schrefl, T.
    Danube Univ Krems, Dept Integrated Sensor Syst, A-3500 Krems, Austria.
    Cuesta-Lopez, S.
    Univ Burgos, Int Res Ctr Crit Raw Mat & Adv Ind Technol, ICCRAM, Burgos 09001, Spain;Fdn Int Ctr Adv Mat & Raw Mat Castilla & Leon, ICAMCyL, Leon 24492, Spain.
    Database of novel magnetic materials for high-performance permanent magnet development2019In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 168, p. 188-202Article in journal (Refereed)
    Abstract [en]

    This paper describes the open Novamag database that has been developed for the design of novel Rare-Earth free/lean permanent magnets. Its main features as software technologies, friendly graphical user interface, advanced search mode, plotting tool and available data are explained in detail. Following the philosophy and standards of Materials Genome Initiative, it contains significant results of novel magnetic phases with high magnetocrystalline anisotropy obtained by three computational high-throughput screening approaches based on a crystal structure prediction method using an Adaptive Genetic Algorithm, tetragonally distortion of cubic phases and tuning known phases by doping. Additionally, it also includes theoretical and experimental data about fundamental magnetic material properties such as magnetic moments, magnetocrystalline anisotropy energy, exchange parameters, Curie temperature, domain wall width, exchange stiffness, coercivity and maximum energy product, that can be used in the study and design of new promising high-performance Rare-Earth free/lean permanent magnets. The results therein contained might provide some insights into the ongoing debate about the theoretical performance limits beyond Rare-Earth based magnets. Finally, some general strategies are discussed to design possible experimental routes for exploring most promising theoretical novel materials found in the database.

  • 22.
    Ortiz, Carlos
    et al.
    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.
    Klintenberg, Mattias
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Materials Theory.
    Data mining and accelerated electronic structure theory as a tool in the search for new functional materials2009In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 44, no 4, p. 1042-1049Article in journal (Refereed)
    Abstract [en]

    A highly accelerated electronic structure implementation and data mining algorithms have been combined with structural data from the inorganic crystal structure database to generate materials properties for about 22,000 inorganic compounds. It is shown how data mining algorithms employed on the database can identify new functional materials with desired materials properties, resulting in a prediction of 136 novel materials with potential for use as detector materials for ionizing radiation. The methodology behind the automatized ab initio approach is presented, results are tabulated and a version of the complete database is made available at the internet web site

  • 23.
    Ramzan, Muhammad
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Li, Y.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Chimata, Raghuveer
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Electronic, mechanical and optical properties of Y2O3 with hybrid density functional (HSE06)2013In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 71, p. 19-24Article in journal (Refereed)
    Abstract [en]

    In this paper, we have investigated the electronic, optical and mechanical properties of the Y2O3 crystal by first-principle calculations based on the density-functional theory. The generalized gradient approximation (GGA-PBE) and hybrid exchange-correlation functional (HSE06) are both used for comparative study. It is found that, the band gap of Y2O3 calculated by HSE06 method (6.0 eV) is in good agreement with the experimental band gap data (5.5 eV), and HSE06 gives better electronic structure description close to experiments. Then we calculate the elastic constants, and derive the corresponding properties i.e.; bulk, shear and Young's moduli, and Poisson's ratio. Our calculated elastic and mechanical properties correspond well with experimental data. Besides, we also obtain the equilibrium lattice and bulk modulus of yttria by fitting the Birch-Murnaghan equation of state. It is found that, the HSE06 well reproduce the experimental lattice parameters, equilibrium volume and bulk modulus of Y2O3. Based on the accurate described crystal and electronic structure and mechanical properties by HSE06 method, the optical properties of this material are also analyzed.

  • 24. Sa, Baisheng
    et al.
    Zhou, Jian
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Sun, Zhimei
    First-principles investigations of electronic and mechanical properties for stable Ge2Sb2Te5 with van der Waals corrections2014In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 82, p. 66-69Article in journal (Refereed)
    Abstract [en]

    The Te-Te weak van der Waals-type bonding plays an important role in Ge2Sb2Te5, a widely investigated phase-change material and a potential topological insulator. In this work, we have studied the electronic and mechanical properties of stable Ge2Sb2Te5 using ab initio calculations with the van der Waals corrections. The results show that the van der Waals corrections combined with hybrid functions improve the descriptions of the electronic structure of stable Ge2Sb2Te5. The band gap of similar to 0.5 eV in very good agreement with the experimental value for stable Ge2Sb2Te5 has been successfully reproduced. Furthermore, we have predicted the elastic constants and mechanical properties of stable trigonal Ge2Sb2Te5.

  • 25.
    Souvatzis, Petros
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Katsnelson, M. I.
    Rudin, S. P.
    The self-consistent ab initio lattice dynamical method2009In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 44, no 3, p. 888-894Article in journal (Refereed)
    Abstract [en]

    We describe a method for calculating temperature dependent phonon spectra self consistently from first principles. The method combines concepts from Born's self-consistent phonon approach with ab initio calculations of accurate interatomic forces in a supercell. Test calculations on the high temperature bcc phase of Ti, Zr, Hf, Sc and Y. as representative examples, reproduce the observed high temperature phonon frequencies with good accuracy. By use of an embedded atom potential we demonstrate the method's relevance in calculating approximate critical temperatures of solid-solid phase transitions for the hcp to bcc transition in Zr.

  • 26.
    Sun, Weiwei
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Hussain, Tanveer
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    De Sarkar, Abir
    Maark, Tuhina Adit
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Luo, Wei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Improvement in the desorption of H-2 from the MgH2 (110) surface by means of doping and mechanical strain2014In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 86, p. 165-169Article in journal (Refereed)
    Abstract [en]

    In this letter, density functional theory has been employed to investigate the release or desorption of hydrogen from the MgH2 (1 1 0) surface. To improve upon the energetics for hydrogen desorption from this system, the effects of strain and doping by Al, Si, Ti have been explored. Both of these two effects have been found to be effective. The strain applied along the X direction induces more prominent effects than along the Y direction. Regarding the doping, the system doped with Al gives the most noticeable effect. The Si doped system shows the least improvement while the Ti doped system lies in between as compared to the other two. The combination of doping and strain effects is found to be more efficacious.

  • 27. Tian, Fu-Yang
    et al.
    Chen, Nan-Xian
    Delczeg, Lorand
    Vitos, Levente
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Interlayer potentials for fcc (111) planes of Pd-Ag random alloys2012In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 63, p. 20-27Article in journal (Refereed)
    Abstract [en]

    Using ab initio alloy theory in combination with the Chen-Mobius inversion method, we obtain the interaction potentials between layers of the face centered cubic (fcc) (111) plane family for elemental Pd and Ag metals and for Pd0.5Ag0.5 random alloy. Based on the interlayer potentials, we investigate properties related to the fcc (111) planes, such as the stacking fault energy, shear elastic constant, surface energy, surface relaxations, and phonon dispersion along the fcc [111] direction. The results agree well with those obtained by fully self-consistent ab initio calculations and also with the available experimental data, indicating that the properties related to the close-packed planes are well described by the interlayer potentials.

  • 28.
    Tian, Fuyang
    et al.
    Univ Sci & Technol Beijing, Inst Appl Phys, Beijing 100083, Peoples R China.;Royal Inst Technol, Dept Mat Sci & Engn, Appl Mat Phys, SE-10044 Stockholm, Sweden..
    Varga, Lajos Karoly
    Inst Solid State Phys & Opt, Wigner Res Ctr Phys, H-1525 Budapest, Hungary..
    Shen, Jiang
    Univ Sci & Technol Beijing, Inst Appl Phys, Beijing 100083, Peoples R China..
    Vitos, Levente
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Royal Inst Technol, Dept Mat Sci & Engn, Appl Mat Phys, SE-10044 Stockholm, Sweden.;Inst Solid State Phys & Opt, Wigner Res Ctr Phys, H-1525 Budapest, Hungary..
    Calculating elastic constants in high-entropy alloys using the coherent potential approximation: Current issues and errors2016In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 111, p. 350-358Article in journal (Refereed)
    Abstract [en]

    The new class of high-entropy alloys (HEAs) materials have shown interesting properties, such as high strength and good ductility. However, HEAs present a great challenge for conventional ab initio calculations and the few available theoretical predictions involve a large degree of uncertainty. An often adopted theoretical tool to study HEAs from first-principles is based on the exact muffin-tin orbitals (EMTO) method in combination with the coherent potentials approximation (CPA), which can handle both chemical and magnetic disorders. Here we assess the performance of EMTO-CPA method in describing the elastic properties of HEAs based on Co, Cr, Fe, Mn, and Ni. We carefully scrutinize the effect of numerical parameters and the impact of various magnetic states on the calculated properties. The theoretical results for the elastic moduli are compared to the available experimental values.

  • 29.
    Tian, Li-Yun
    et al.
    Royal Inst Technol, Dept Mat Sci & Engn, Appl Mat Phys, SE-10044 Stockholm, Sweden.;Dalian Univ Technol, Minist Educ, Key Lab Mat Modificat Laser Ion & Electron Beams, Dalian 116024, Peoples R China..
    Ye, Li-Hua
    Chinese Acad Sci, Inst Met Res, 72 Wenhua Rd, Shenyang 110016, Peoples R China..
    Hu, Qing-Miao
    Chinese Acad Sci, Inst Met Res, 72 Wenhua Rd, Shenyang 110016, Peoples R China..
    Lu, Song
    Royal Inst Technol, Dept Mat Sci & Engn, Appl Mat Phys, SE-10044 Stockholm, Sweden..
    Zhao, Jijun
    Dalian Univ Technol, Minist Educ, Key Lab Mat Modificat Laser Ion & Electron Beams, Dalian 116024, Peoples R China..
    Vitos, Levente
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Royal Inst Technol, Dept Mat Sci & Engn, Appl Mat Phys, SE-10044 Stockholm, Sweden.; Div MWigner Res Ctr Phys, Res Inst Solid State Phys & Opt, POB 49, H-1525 Budapest, Hungary..
    CPA descriptions of random Cu-Au alloys in comparison with SQS approach2017In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 128, p. 302-309Article in journal (Refereed)
    Abstract [en]

    The lattice constant, formation enthalpy, and elastic parameters of Cu1-xAux (0 <= x <= 1) alloys in the face centered cubic crystallographic phase are investigated by using the first-principles exact muffin-tin orbitals and plane-wave pseudopotential methods in order to explore the effect of alloying with special focus on the impact of local lattice distortion (LLD) on the above properties. The compositional disorder is treated within the framework of the coherent potential approximation (CPA) and the special quasi-random structure (SQS) scheme. Calculations based on SQS and CPA show that, while LLD lowers significantly the formation enthalpy of Cu1-xAux due to the large size mismatch between Cu and Au atoms, it has negligible influence on the lattice constants and elastic parameters. These findings confirm the reliability of CPA for computing the enthalpy changes upon isotropic and unisotropic lattice distortions in disordered alloys with sizable atomic size differences.

  • 30.
    Vitos, Levente
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Larsson, Karin
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry, Inorganic Chemistry.
    Johansson, Börje
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Hanson, Magnus
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Materials Science.
    Hogmark, Sture
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Materials Science.
    An atomistic approach to the initiation mechanism of galling2006In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 37, no 3, p. 193-197Article in journal (Refereed)
    Abstract [en]

    Sliding metallic contacts are accompanied by a severe wear phenomenon named galling. This is manifested in adhesion followed by a substantial increase of friction and subsequent deterioration of the contact surfaces. Experiments on titanium- and vanadium-nitride coated surfaces slid against steels indicate that VN exhibits low friction and improved galling characteristics, clearly outperforming the widely used TiN coating. Using first principles simulations, based on the exact muffin-tin orbital and pseudopotential methods, we present an insight to the atomic level processes initiating galling at Ti(V)N-Fe interfaces. It is found that the equilibrium atomic-scale contacts between nitrides and Fe are adhesive. We demonstrate that the close-packed (001) VN-Fe interface exhibits a lower atomic-level roughness and a reduced atomic-friction coefficient than that in the case of TiN. These theoretical results indicate that VN is less prone to galling compared to TiN.

  • 31. Xu, Jingcheng
    et al.
    Zhao, Jijun
    Korzhavyi, Pavel
    Johansson, Börje
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ab initio calculations of elastic properties of Fe-Cr-W alloys2014In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 84, p. 301-305Article in journal (Refereed)
    Abstract [en]

    Reduced activation ferritic/martensitic (RAFM) steels are considered as the primary candidate for the blanket module in International Thermonuclear Experimental Reactor (ITER), and the basic composition of RAFM steels is Fe-Cr-W alloy. Using the exact muffin-tin orbitals method (EMTO) combined with coherent potential approximation (CPA), we investigated composition dependence of elastic properties for Fe-Cr-W random alloys in the composition range of 7.8-10.0 wt.% of Cr and 1.0-2.0 wt.% of W. Bulk modulus, shear modulus, Young's modulus, B/G ratio, and Poisson ratio are discussed as functions of ternary composition. The elastic moduli of Fe-Cr-W alloys increase with chromium content in the studied range of alloy compositions, the effect of tungsten is slight. (C) 2013 Elsevier B. V. All rights reserved.

  • 32. Zarechnaya, E. Yu.
    et al.
    Skorodumova, Natalia V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Condensed Matter Theory.
    Simak, S. I.
    Johansson, Börje
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Condensed Matter Theory.
    Isaev, E. I.
    Theoretical study of linear monoatomic nanowires, dimer and bulk of Cu, Ag, Au, Ni, Pd and Pt2008In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 43, no 3, p. 522-530Article in journal (Refereed)
    Abstract [en]

    The binding and electronic properties of monoatomic nanowires, dimers and bulk structures of Cu, Ag, Au and Ni, Pd, Pt have been studied by the projector augmented-wave method (PAW) within the density functional theory (DFT) using the local density approximation (LDA) as well as generalized gradient approximation (GGA) in both Perdew-Wang (PW91) and Perdew-Burke-Ernzerhof (PBE) parameterizations. Our results show that the formation of atomic chains is not equally plausible for all the studied elements. In agreement with experimental observations Pt and An stand out as most likely elements to form monoatomic wires. Changes in the electronic structure and magnetic properties of metal chains at stretching are analyzed.

  • 33. Zhang, Hualei
    et al.
    Johansson, Börje
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ahuja, Rajeev
    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.
    First-principles study of solid-solution hardening in steel alloys2012In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 55, p. 269-272Article in journal (Refereed)
    Abstract [en]

    Materials with excellent mechanical properties, such as light mass combined with remarkable hardness and toughness, are technologically important not least for automotive and other transport applications. Solid solution strengthening, due to dislocation pinning by impurities, is an effective route to enhance the intrinsic hardness of alloys. In the present work, we use advanced quantum theory to reveal the mechanical characteristics of iron alloys within and beyond their thermodynamic stability fields. Among the considered alloying elements, magnesium strongly reduces the density of the host alloys and significantly enhances the hardness. Our findings suggest that stainless steel grades containing a few percent of magnesium are promising engineering materials for high-strength and light-weight designs.

  • 34.
    Zhao, Wenyue
    et al.
    Beihang Univ, Sch Mat Sci & Engn, Key Lab Aerosp Mat & Performance,Minist Ind & Inf, Minist Educ,Key Lab High Temp Struct Mat & Coatin, Beijing 100191, Peoples R China;Beihang Univ, Ctr Integrated Computat Mat Engn, Int Res Inst Multidisciplinary Sci, Beijing 100191, Peoples R China.
    Li, Wei
    Royal Inst Technol, Dept Mat Sci & Engn, Appl Mat Phys, SE-10044 Stockholm, Sweden.
    Li, Xiaoqing
    Royal Inst Technol, Dept Mat Sci & Engn, Appl Mat Phys, SE-10044 Stockholm, Sweden.
    Gong, Shengkai
    Beihang Univ, Sch Mat Sci & Engn, Key Lab Aerosp Mat & Performance,Minist Ind & Inf, Minist Educ,Key Lab High Temp Struct Mat & Coatin, Beijing 100191, Peoples R China.
    Vitos, Levente
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Royal Inst Technol, Dept Mat Sci & Engn, Appl Mat Phys, SE-10044 Stockholm, Sweden;Wigner Res Ctr Phys, Res Inst Solid State Phys & Opt, POB 49, H-1525 Budapest, Hungary.
    Sun, Zhimei
    Beihang Univ, Sch Mat Sci & Engn, Key Lab Aerosp Mat & Performance,Minist Ind & Inf, Minist Educ,Key Lab High Temp Struct Mat & Coatin, Beijing 100191, Peoples R China;Beihang Univ, Ctr Integrated Computat Mat Engn, Int Res Inst Multidisciplinary Sci, Beijing 100191, Peoples R China.
    Thermo-mechanical properties of Ni-Mo solid solutions: A first-principles study2019In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 158, p. 140-148Article in journal (Refereed)
    Abstract [en]

    The mechanical strength of Ni-based single-crystal superalloys under service condition is related to the thermomechanical properties of the disordered gamma matrix. Here we use density functional theory and quasi-harmonic approximation to determine the temperature-dependent bulk moduli and generalized stacking fault energies (GSFEs) of Ni-Mo solid solutions. We show that the increasing temperatures between 1000 K and 1400 K cause evident reductions in the bulk moduli and planar fault energies of Ni-Mo alloys. Furthermore, their negative slopes versus temperature are gradually diminished with increasing Mo concentration except that of the unstable stacking fault energy. Adopting recent theoretical models for twinning based on GSFE, increasing temperature enhances the twinnability of low-Mo alloys but has limited influences in the case of high-Mo alloys. The composition-dependent thermal expansion, the thermal electronic excitation and the magnetic transition are shown to be the main factors rendering the complex variations in the elastic properties and twinning behavior of Ni-Mo solid solution with temperature.

1 - 34 of 34
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