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  • 101.
    Isaev, E.I.
    et al.
    Moscow Technological University.
    Ahuja, R.
    Uppsala University.
    Simak, Sergey
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics.
    Lichtenstein, A.I.
    Universität Hamburg.
    Vekilov, Yu. Kh.
    Moscow Technological University.
    Johansson, B.
    Uppsala University.
    Abrikosov, Igor
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics.
    Anomalously enhanced superconductivity and ab initio lattice dynamics in transition metal carbides and nitrides2005In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 72, no 6, p. 4515-Article in journal (Refereed)
    Abstract [en]

    The lattice dynamics for the monocarbides and mononitrides of the early transition metals has been studied using first-principles density functional perturbation theory. It is shown that the superconductivity of transition metal carbides is directly related to anomalies in the phonon spectra which in their turn are connected to the number of valence electrons. The calculated electron-phonon interaction constants are in excellent agreement with experimental data. Superconductivity is considerably enhanced for substitutional M Cx N1-x alloys. We also predict that perfect VC in the sodium chloride structure (B1) is a superconductor with a transition temperature Tc =11.5 K. The experimental failure to sythesize some transition metal carbides and nitrides within the B1 structure is connected to their dynamical instability. © 2005 The American Physical Society.

  • 102.
    Isaev, E.I.
    et al.
    Theoretical Physics Department, Moscow Stt. Inst. Steel and Alloys, 4, Leninskii Prospect, Moscow 119049, Russian Federation.
    Lichtenstein, A.I.
    Research Institute of Materials, Nijmegen University, 1 Toernooiveld, 6525 ED Nijmegen, Netherlands.
    Vekilov, Yu.Kh.
    Theoretical Physics Department, Moscow Stt. Inst. Steel and Alloys, 4, Leninskii Prospect, Moscow 119049, Russian Federation.
    Smirnova, E.A.
    Theoretical Physics Department, Moscow Stt. Inst. Steel and Alloys, 4, Leninskii Prospect, Moscow 119049, Russian Federation.
    Abrikosov, Igor
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics .
    Simak, S.I.
    Condensed Matter Theory Group, Uppsala University, SE-751 21 Uppsala, Sweden.
    Ahuja, R.
    Condensed Matter Theory Group, Uppsala University, SE-751 21 Uppsala, Sweden.
    Johansson, B.
    Condensed Matter Theory Group, Uppsala University, SE-751 21 Uppsala, Sweden, Dept. of Mat. Sci. and Engineering, Royal Institute of Technology (KTH), SE-100 44 Stockholm, Sweden.
    Ab initio phonon calculations for L12 Ni3Al and B2 NiAl2004In: Solid State Communications, ISSN 0038-1098, E-ISSN 1879-2766, Vol. 129, no 12, p. 809-814Article in journal (Refereed)
    Abstract [en]

    The phonon spectra and phonon density of states of the Ni3Al and NiAl intermetallic compounds are calculated from first principles using the linear response method in conjunction with ultrasoft pseudopotentials. The calculated phonon dispersion curves are in good agreement with available experimental results from inelastic neutron scattering. © 2003 Elsevier Ltd. All rights reserved.

  • 103.
    Isaev, E.I.
    et al.
    Moscow State Institute of Steel and Alloys Technological University, Moscow.
    Simak, Sergey
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics .
    Abrikosov, Igor
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics .
    Ahuja, R.
    Uppsala universitet.
    Vekilov, Yu.Kh.
    Moscow State Institute of Steel and Alloys Technological University, Moscow.
    Katsnelson, M.I.
    Radboud University of Nujmegen, The Netherlands.
    Lichtenstein, A.I.
    Universitaet, Hamburg.
    Johansson, B.
    KTH, och Uppsala universitet.
    Phonon related properties of transition metals, their carbides, and nitrides: A first-principles study2007In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 101, p. 123519-1-12351918Article in journal (Refereed)
    Abstract [en]

      

  • 104.
    Isaev, Eyvas
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics . Linköping University, The Institute of Technology.
    Simak, Sergey
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics . Linköping University, The Institute of Technology.
    Mikhaylushkin, Arkady
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics . Linköping University, The Institute of Technology.
    Vekilov, Yu. Kh.
    Moscow State Institute Steel and Alloys.
    Zarechnaya, E. Yu.
    Harvard University.
    Dubrovinsky, L.
    University of Bayreuth.
    Dubrovinskaia, N.
    University of Heidelberg.
    Merlini, M.
    University of Milan.
    Hanfland, M.
    ESRF.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics . Linköping University, The Institute of Technology.
    Impact of lattice vibrations on equation of state of the hardest boron phase2011In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 83, no 13, p. 132106-Article in journal (Refereed)
    Abstract [en]

    An accurate equation of state (EOS) is determined for the high-pressure orthorhombic phase of boron, B(28), experimentally as well as from ab initio calculations. The unique feature of our experiment is that it is carried out on the single crystal of B(28). In theory, we take into consideration the lattice vibrations, often neglected in first-principles simulations. We show that the phonon contribution has a profound effect on the EOS of B(28), giving rise to anomalously low values of the pressure derivative of the bulk modulus and greatly improving the agreement between theory and experiment.

  • 105.
    Isaeva, L E
    et al.
    Moscow MV Lomonosov State University.
    Bazhanov, D I
    Moscow MV Lomonosov State University.
    Isaev, Eyvas
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics . Linköping University, The Institute of Technology.
    Eremeev, S V
    Russian Academy of Science.
    Kulkova, S E
    Russian Academy of Science.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics . Linköping University, The Institute of Technology.
    Dynamic stability of palladium hydride: An ab initio study2011In: INTERNATIONAL JOURNAL OF HYDROGEN ENERGY, ISSN 0360-3199, Vol. 36, no 1, p. 1254-1258Article in journal (Refereed)
    Abstract [en]

    We present results of our ab initio studies of electronic and dynamic properties of ideal palladium hydride PdH and its vacancy ordered defect phase Pd(3)VacH(4) ("Vac" - vacancy on palladium site) with L1(2) crystal structure found experimentally and studied theoretically. Quantum and thermodynamic properties of these hydrides, such as phonon dispersion relations and the vacancy formation enthalpies have been studied. Dynamic stability of the defect phase Pd(3)VacH(4) with respect to different site occupation of hydrogen atoms at the equilibrium state and under pressure was analyzed. It was shown that positions of hydrogen atoms in the defect phase strongly affect its stability and may be a reason for further phase transitions in the defect phase.

  • 106.
    Isaeva, L.
    et al.
    Uppsala University, Sweden.
    Hellman, Olle
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. CALTECH, CA 91125 USA.
    Lashley, J. C.
    Los Alamos National Lab, NM 87545 USA.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Eriksson, O.
    Uppsala University, Sweden.
    Dynamic stabilization of cubic AuZn2015In: MATERIALS TODAY-PROCEEDINGS, ELSEVIER SCIENCE BV , 2015, Vol. 2, p. 569-572Conference paper (Refereed)
    Abstract [en]

    A recently developed temperature-dependent effective potential method is employed to study the martensitic phase transformation in AuZn. This method is based on ab initio molecular dynamics and allows to obtain finite-temperature lattice vibrational properties. We show that the transversal acoustic TA(2)[110] mode associated with the phase transition is stabilized at 300 K. Temperature evolution of single-phonon dynamic structure factor at the wave vector q= 1/3[1,1,0], associated with phonon softening and Fermi surface nesting, was also studied. (C) 2015 The Authors. Published by Elsevier Ltd.

  • 107.
    Ivády, Viktor
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Hungarian Acad Sci, Hungary.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Natl Univ Sci and Technol MISIS, Russia.
    Gali, Adam
    Hungarian Acad Sci, Hungary; Budapest Univ Technol and Econ, Hungary.
    First principles calculation of spin-related quantities for point defect qubit research2018In: NPJ COMPUTATIONAL MATERIALS, ISSN 2057-3960, Vol. 4, article id 76Article, review/survey (Refereed)
    Abstract [en]

    Point defect research in semiconductors has gained remarkable new momentum due to the identification of special point defects that can implement qubits and single photon emitters with unique characteristics. Indeed, these implementations are among the few alternatives for quantum technologies that may operate even at room temperature, and therefore discoveries and characterization of novel point defects may highly facilitate future solid state quantum technologies. First principles calculations play an important role in point defect research, since they provide a direct, extended insight into the formation of the defect states. In the last decades, considerable efforts have been made to calculate spin-dependent properties of point defects from first principles. The developed methods have already demonstrated their essential role in quantitative understanding of the physics and application of point defect qubits. Here, we review and discuss accuracy aspects of these novel ab initio methods and report on their most relevant applications for existing point defect qubits in semiconductors. We pay attention to the advantages and limitations of the methodological solutions and highlight additional developments that are expected in the near future. Moreover, we discuss the opportunity of a systematic search for potential point defect qubits, as well as the possible development of predictive spin dynamic simulations facilitated by ab initio calculations of spin-dependent quantities.

  • 108.
    Ivády, Viktor
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Gali, A
    Hungarian Academic Science, Hungary.
    Role of screening in the density functional applied to transition-metal defects in semiconductors2013In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 87, no 20Article in journal (Refereed)
    Abstract [en]

    We study selected transition-metal-related point defects in silicon and silicon carbide semiconductors by a range-separated hybrid density functional (HSE06). We find that HSE06 does not fulfill the generalized Koopmans' theorem for every defect, which is due to the self-interaction error in the functional in such cases. Restoring the so-called generalized Koopmans' condition with a simple correction in the functional can eliminate this error and brings the calculated charge transition levels remarkably close to the experimental data as well as to the calculated quasiparticle levels from many-body perturbation theory.

  • 109.
    Ivády, Viktor
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Gali, Adam
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Theoretical investigation of the single photon emitter carbon antisite-vacancy pair in 4H-SiC2014In: SILICON CARBIDE AND RELATED MATERIALS 2013, PTS 1 AND 2, Trans Tech Publications , 2014, Vol. 778-780, p. 495-498Conference paper (Refereed)
    Abstract [en]

    Well addressable and controllable point defects in device friendly semiconductors are desired for quantum computational and quantum informational processes. Recently, such defect, an ultra-bright single photon emitter, the carbon antisite - vacancy pair, was experimentally investigated in 4H-SiC. In our theoretical work, based on ab initio calculation and group theory analysis, we provide a deeper understanding of the features of the electronic structures and the luminescence process of this defect.

  • 110.
    Ivády, Viktor
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Armiento, Rickard
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Szasz, Krisztian
    Hungarian Academic Science, Hungary Eotvos Lorand University, Hungary .
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Gali, Adam
    Hungarian Academic Science, Hungary Budapest University of Technology and Econ, Hungary .
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Theoretical unification of hybrid-DFT and DFT plus U methods for the treatment of localized orbitals2014In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 90, no 3, p. 035146-Article in journal (Refereed)
    Abstract [en]

    Hybrid functionals serve as a powerful practical tool in different fields of computational physics and quantum chemistry. On the other hand, their applicability for the case of correlated d and f orbitals is still questionable and needs more considerations. In this article we formulate the on-site occupation dependent exchange correlation energy and effective potential of hybrid functionals for localized states and connect them to the on-site correction term of the DFT+ U method. The resultant formula indicates that the screening of the onsite electron repulsion is governed by the ratio of the exact exchange in hybrid functionals. Our derivation provides a theoretical justification for adding a DFT+ U-like on-site potential in hybrid-DFT calculations to resolve issues caused by overscreening of localized states. The resulting scheme, hybrid DFT+ V-w, is tested for chromium impurity in wurtzite AlN and vanadium impurity in 4H-SiC, which are paradigm examples of systems with different degrees of localization between host and impurity orbitals.

  • 111.
    Ivády, Viktor
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Hungarian Academic Science, Hungary.
    Davidsson, Joel
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Nguyen, Tien Son
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Ohshima, Takeshi
    National Institute Quantum and Radiol Science and Technology, Japan.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. National University of Science and Technology MISIS, Russia.
    Gali, Adam
    Hungarian Academic Science, Hungary; Budapest University of Technology and Econ, Hungary.
    Identification of Si-vacancy related room-temperature qubits in 4H silicon carbide2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, no 16, article id 161114Article in journal (Refereed)
    Abstract [en]

    The identification of a microscopic configuration of point defects acting as quantum bits is a key step in the advance of quantum information processing and sensing. Among the numerous candidates, silicon-vacancy related centers in silicon carbide (SiC) have shown remarkable properties owing to their particular spin-3/2 ground and excited states. Although, these centers were observed decades ago, two competing models, the isolated negatively charged silicon vacancy and the complex of negatively charged silicon vacancy and neutral carbon vacancy [Phys. Rev. Lett. 115, 247602 (2015)], are still argued as an origin. By means of high-precision first-principles calculations and high-resolution electron spin resonance measurements, we here unambiguously identify the Si-vacancy related qubits in hexagonal SiC as isolated negatively charged silicon vacancies. Moreover, we identify the Si-vacancy qubit configurations that provide room-temperature optical readout.

  • 112.
    Ivády, Viktor
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Hungarian Academic Science, Hungary.
    Gali, Adam
    Hungarian Academic Science, Hungary; Budapest University of Technology and Econ, Hungary.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. National University of Science and Technology MISIS, Russia.
    Hybrid-DFT + V-w method for band structure calculation of semiconducting transition metal compounds: the case of cerium dioxide2017In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 29, no 45, article id 454002Article in journal (Refereed)
    Abstract [en]

    Hybrid functionals non-local exchange-correlation potential contains a derivative discontinuity that improves on standard semi-local density functional theory (DFT) band gaps. Moreover, by careful parameterization, hybrid functionals can provide self-interaction reduced description of selected states. On the other hand, the uniform description of all the electronic states of a given system is a known drawback of these functionals that causes varying accuracy in the description of states with different degrees of localization. This limitation can be remedied by the orbital dependent exact exchange extension of hybrid functionals; the hybrid-DFT + V-w method (Ivady et al 2014 Phys. Rev. B 90 035146). Based on the analogy of quasi-particle equations and hybrid-DFT single particle equations, here we demonstrate that parameters of hybrid-DFT + V-w functional can be determined from approximate theoretical quasi-particle spectra without any fitting to experiment. The proposed method is illustrated on the charge self-consistent electronic structure calculation for cerium dioxide where itinerant valence states interact with well-localized 4f atomic like states, making this system challenging for conventional methods, either hybrid-DFT or LDA + U, and therefore allowing for a demonstration of the advantages of the proposed scheme.

  • 113.
    Ivády, Viktor
    et al.
    Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Hungarian Academic Science, Hungary.
    Klimov, Paul V.
    University of Chicago, IL 60637 USA.
    Miao, Kevin C.
    University of Chicago, IL 60637 USA.
    Falk, Abram L.
    University of Chicago, IL 60637 USA; IBM TJ Watson Research Centre, NY 10598 USA.
    Christle, David J.
    University of Chicago, IL 60637 USA.
    Szasz, Krisztian
    Hungarian Academic Science, Hungary.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. National University of Science and Technology MISIS, Russia.
    Awschalom, David D.
    University of Chicago, IL 60637 USA.
    Gali, Adam
    Hungarian Academic Science, Hungary; Budapest University of Technology and Econ, Hungary.
    High-Fidelity Bidirectional Nuclear Qubit Initialization in SiC2016In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 117, no 22, article id 220503Article in journal (Refereed)
    Abstract [en]

    Dynamic nuclear polarization (DNP) is an attractive method for initializing nuclear spins that are strongly coupled to optically active electron spins because it functions at room temperature and does not require strong magnetic fields. In this Letter, we theoretically demonstrate that DNP, with near-unity polarization efficiency, can be generally realized in weakly coupled electron spin-nuclear spin systems. Furthermore, we theoretically and experimentally show that the nuclear spin polarization can be reversed by magnetic field variations as small as 0.8 Gauss. This mechanism offers new avenues for DNP-based sensors and radio-frequency free control of nuclear qubits.

  • 114.
    Ivády, Viktor
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology. Hungarian Academic Science, Hungary.
    Simon, Tamas
    Budapest University of Technology and Econ, Hungary.
    Maze, Jeronimo R.
    Pontificia University of Catolica Chile, Chile.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology. National University of Science and Technology MISIS, Russia; Tomsk State University, Russia.
    Gali, Adam
    Hungarian Academic Science, Hungary; Budapest University of Technology and Econ, Hungary.
    Pressure and temperature dependence of the zero-field splitting in the ground state of NV centers in diamond: A first-principles study2014In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 90, no 23, p. 235205-Article in journal (Refereed)
    Abstract [en]

    Nitrogen-vacancy centers in diamond (NV) attract great attention because they serve as a tool in many important applications. The NV center has a polarizable spin S = 1 ground state and its spin state can be addressed by optically detected magnetic resonance (ODMR) techniques. The m(S) = 0 and m(S) = +/- 1 spin levels of the ground state are separated by about 2.88 GHz in the absence of an external magnetic field or any other perturbations. This zero-field splitting (ZFS) can be probed by ODMR. As this splitting changes as a function of pressure and temperature, the NV center might be employed as a sensor operating at the nanoscale. Therefore, it is of high importance to understand the intricate details of the pressure and temperature dependence of this splitting. Here we present an ab initio theory of the ZFS of the NV center as a function of external pressure and temperature including detailed analysis on the contributions of macroscopic and microscopic effects. We found that the pressure dependence is governed by the change in the distance between spins as a consequence of the global compression and the additional local structural relaxation. The local structural relaxation contributes to the change of ZFS with the same magnitude as the global compression. In the case of temperature dependence of ZFS, we investigated the effect of macroscopic thermal expansion as well as the consequent change of the microscopic equilibrium positions. We could conclude that theses effects are responsible for about 15% of the observed decrease of ZFS.

  • 115.
    Ivády, Viktor
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Hungarian Academic Science, Hungary.
    Szasz, Krisztian
    Hungarian Academic Science, Hungary.
    Falk, Abram L.
    University of Chicago, IL 60637 USA; IBM Corp, NY 10598 USA.
    Klimov, Paul V.
    University of Chicago, IL 60637 USA; University of Calif Santa Barbara, CA 93106 USA.
    Christle, David J.
    University of Chicago, IL 60637 USA; University of Calif Santa Barbara, CA 93106 USA.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. National University of Science and Technology MISIS, Russia; Tomsk State University, Russia.
    Awschalom, David D.
    University of Chicago, IL 60637 USA.
    Gali, Adam
    Hungarian Academic Science, Hungary; Budapest University of Technology and Econ, Hungary.
    Theoretical model of dynamic spin polarization of nuclei coupled to paramagnetic point defects in diamond and silicon carbide2015In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 92, no 11, p. 115206-Article in journal (Refereed)
    Abstract [en]

    Dynamic nuclear spin polarization (DNP) mediated by paramagnetic point defects in semiconductors is a key resource for both initializing nuclear quantum memories and producing nuclear hyperpolarization. DNP is therefore an important process in the field of quantum-information processing, sensitivity-enhanced nuclear magnetic resonance, and nuclear-spin-based spintronics. DNP based on optical pumping of point defects has been demonstrated by using the electron spin of nitrogen-vacancy (NV) center in diamond, and more recently, by using divacancy and related defect spins in hexagonal silicon carbide (SiC). Here, we describe a general model for these optical DNP processes that allows the effects of many microscopic processes to be integrated. Applying this theory, we gain a deeper insight into dynamic nuclear spin polarization and the physics of diamond and SiC defects. Our results are in good agreement with experimental observations and provide a detailed and unified understanding. In particular, our findings show that the defect electron spin coherence times and excited state lifetimes are crucial factors in the entire DNP process.

  • 116.
    Johansson, B
    et al.
    Royal Institute of Technology.
    Ruban, A V
    Royal Institute of Technology.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Comment on "Thermal Signatures of the Kondo Volume Collapse in Cerium": in Physical Review Letters, vol 102, 1896012009In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 102, no 18, p. 189601-Article in journal (Other academic)
    Abstract [en]

    A Comment on the Letter by M. J. Lipp et al., Phys. Rev. Lett. 101, 165703 (2008).

  • 117.
    Johansson, Leif I.
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Armiento, Rickard
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Avila, Jose
    Synchrotron SOLEIL, France .
    Xia, Chao
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Lorcy, Stephan
    Synchrotron SOLEIL, France .
    Igor A., Abrikosov
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Asensio, Maria C.
    Synchrotron SOLEIL, France .
    Virojanadara, Chariya
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Multiple π-bands and Bernal stacking of multilayer graphene on C-face SiC, revealed by nano-Angle Resolved Photoemission2014In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 4, no 4157Article in journal (Refereed)
    Abstract [en]

    Only a single linearly dispersing π-band cone, characteristic of monolayer graphene, has so far been observed in Angle Resolved Photoemission (ARPES) experiments on multilayer graphene grown on C-face SiC. A rotational disorder that effectively decouples adjacent layers has been suggested to explain this. However, the coexistence of μm-sized grains of single and multilayer graphene with different azimuthal orientations and no rotational disorder within the grains was recently revealed for C-face graphene, but conventional ARPES still resolved only a single π-band. Here we report detailed nano-ARPES band mappings of individual graphene grains that unambiguously show that multilayer C-face graphene exhibits multiple π-bands. The band dispersions obtained close to the K-point moreover clearly indicate, when compared to theoretical band dispersion calculated in the framework of the density functional method, Bernal (AB) stacking within the grains. Thus, contrary to earlier claims, our findings imply a similar interaction between graphene layers on C-face and Si-face SiC.

  • 118.
    Jönsson, Johan
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Ekholm, Marcus
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Bykov, Maxim
    Univ Bayreuth, Germany.
    Dubrovinsky, Leonid
    Univ Bayreuth, Germany.
    van Smaalen, Sander
    Univ Bayreuth, Germany.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Natl Univ Sci and Technol MISIS, Russia.
    Inverse pressure-induced Mott transition in TiPO42019In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, no 24, article id 245132Article in journal (Refereed)
    Abstract [en]

    TiPO4 shows interesting structural and magnetic properties as temperature and pressure are varied, such as a spin-Peierls phase transition and the development of incommensurate modulations of the lattice. Recently, high-pressure experiments for TiPO4 reported two structural phases appearing at high pressures, the so-called phases IV and V [M. Bykov et al., Angew. Chem. Int. Ed. 55, 15053 (2016).]. The latter was shown to include the first example of fivefold O-coordinated P atoms in an inorganic phosphate compound. In this work, we characterize the electronic structure and other physical properties of these phases by means of ab initio calculations and investigate the structural transition. We find that the appearance of phases IV and V coincides with a collapse of the Mott insulating gap and quenching of magnetism in phase III as pressure is applied. Remarkably, our calculations show that in the high-pressure phase V, these features reappear, leading to an antiferromagnetic Mott insulating phase, with robust local moments.

  • 119.
    Khvan, A. V.
    et al.
    NUST MISIS, Russia.
    Babkina, T.
    Lomonosov Moscow State Univ, Russia.
    Dinsdale, A. T.
    Hampton Thermodynam Ltd, England.
    Uspenskaya, I. A.
    Lomonosov Moscow State Univ, Russia.
    Fartushna, I. V.
    NUST MISIS, Russia.
    Druzhinina, A. I.
    Lomonosov Moscow State Univ, Russia.
    Syzdykova, A. B.
    NUST MISIS, Russia.
    Belov, M. P.
    NUST MISIS, Russia.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. NUST MISIS, Russia.
    Thermodynamic properties of tin: Part I Experimental investigation, ab-initio modelling of alpha-, beta-phase and a thermodynamic description for pure metal in solid and liquid state from 0 K2019In: Calphad, ISSN 0364-5916, E-ISSN 1873-2984, Vol. 65, p. 50-72Article in journal (Refereed)
    Abstract [en]

    Thermodynamic data for crystalline white and grey tin were assessed using an extended Einstein model from 0 K. Ab-initio simulations in the framework of density functional theory (DFT) with the quasiharmonic approximation (QHA) were carried out to define the heat capacities for both phases of tin from 0 K up to room temperatures. Good agreement was observed between theoretical and experimental heat capacities, which makes it possible to combine theoretical and experimental data to determine the standard entropies. Data for the liquid phase were described using a two state model. During the assessment, careful analysis of the experimental data was carried out. In order to fulfil the need for a precise evaluation of S-298(o) we needed to use an additional technique using multiple Einstein functions, which allows the experimental heat capacity and enthalpy data for the solid phase to be approximated accurately from 0 K up to the melting point and to estimate solid phase transition entropy and enthalpy which are difficult to measure due to a high activation barrier. Additional measurements of heat capacity were carried out where existing data were scarce.

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  • 120.
    Kissavos, Andreas E.
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Shallcross, Sam
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Kaufman, L.
    CALPHAD, Brookline, Massachusetts, USA.
    Grånäs, Oscar
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Ruban, A. V.
    Applied Material Science, Royal Institute of Technology, Stockholm, Sweden.
    Abrikosov, Igor A.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Thermodynamics of ordered and disordered phases in the binary Mo-Ru system2007In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 75, no 18, p. 184203-Article in journal (Refereed)
    Abstract [en]

    Wehave performed ab initio calculations of the mixing enthalpy forthe Mo-Ru alloy system. Both completely random alloys on thefcc, bcc, and hcp lattices as well as ordered andpartially ordered structures based on the hcp lattice and a phase have been examined. Further, we have performed aground-state search for the Ru-rich region using ab initio derivedeffective interactions, and find a series of structures below thetie line of the simple compounds. Using the structures fromthis ground-state search, we are able to make an estimationof the contribution to the total energy due to orderingeffects in this system. We find unusually large deviations betweencalculated and experimental values of the mixing enthalpy for Ru-richhcp alloys. Our calculations indicate, in agreement with experiment, thatthere are ordering trends in the system. However, even underassumption of maximal order theoretical results differ substantially from theexperiment. Possible reasons for the disagreement are discussed.

  • 121.
    Kissavos, Andreas E.
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics . Linköping University, The Institute of Technology.
    Shallcross, Sam
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Meded, V.
    Department of Physics, Uppsala University, Uppsala, Sweden.
    Kaufman, L.
    Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA.
    Abrikosov, Igor A.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics . Linköping University, The Institute of Technology.
    A critical test of ab initio and CALPHAD methods: The structural energy difference between bcc and hcp molybdenum2005In: Calphad, ISSN 0364-5916, E-ISSN 1873-2984, Vol. 29, no 1, p. 17-23Article in journal (Refereed)
    Abstract [en]

    Ab initio calculations of the enthalpy of formation of bcc, fcc, and hcp Ru–Mo alloys have been performed for random, ordered, and partially ordered structures. The lattice stability of the bcc and hcp forms of Mo is isolated in order to compare the hcp–bcc difference calculated by ab initio and CALPHAD methods with experimental measurements of the enthalpy of formation of Ru–Mo alloys. The significance of this comparison in calculating the Mo–Ru phase diagram is illustrated. The results of these considerations suggest a rational method for coupling ab initio and CALPHAD techniques might be utilization of the ab initio methods for calculation of the isostructural energies of formation for binary bcc, hcp, and fcc solutions while retaining the CALPHAD lattice stabilities in the calculation of phase diagrams.

  • 122.
    Kissavos, Andreas E.
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics . Linköping University, The Institute of Technology.
    Simak, Sergey I.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics . Linköping University, The Institute of Technology.
    Olsson, P.
    Department of Neutron Research, Ångström Laboratory, Uppsala University, Uppsala, Sweden.
    Vitos, L.
    Applied Material Physics, Department of Materials Science and Engineering, Royal Institute of Technology, Stockholm, Sweden.
    Abrikosov, Igor A.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics . Linköping University, The Institute of Technology.
    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 total energy calculations for systems with magnetic and chemical disorder, 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.

  • 123.
    Kissavos, Andreas
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics.
    Vitos, L.
    Applied Materials Physics, Department of Materials Science and Engineering, Royal Institute of Technology, SE-10044, Stockholm, Sweden .
    Abrikosov, Igor
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics.
    Energy dependence of the Exact Muffin-Tin Orbitals structure constants2007In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 75, no 11, p. 115117-Article in journal (Refereed)
    Abstract [en]

    We investigate the energy dependence of the exact muffin-tin-orbital slope matrix in the complex energy plane. Analytic expressions for the asymptotic behavior of the slope matrix and its first energy derivative for large imaginary energies are given. We demonstrate that a two-center Taylor type expansion of the slope matrix accurately reproduces the exact values within a complex energy range covering the usual energy window used in electronic structure calculations. As an application, we study the composition dependence of the lattice parameters of the MgY binary system, a candidate material for hydrogen storage applications.

  • 124.
    Krasilnikov, O. M.
    et al.
    NUST MISIS, Russia.
    Lugovskoy, A. V
    NUST MISIS, Russia; Radboud Univ Nijmegen, Netherlands.
    Dikan, V
    NUST MISIS, Russia; CSIC, Spain.
    Belov, M. P.
    NUST MISIS, Russia.
    Vekilov, Yu Kh
    NUST MISIS, Russia.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. NUST MISIS, Russia.
    Nonlinear elasticity of epsilon -Fe: The pressure effect2019In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, no 18, article id 184101Article in journal (Refereed)
    Abstract [en]

    Description of elasticity of iron at the ultrahigh pressures is a challenging task for physics, with a potential strong impact on other branches of science. In the present work, we calculate the elastic properties of hcp iron in the pressure range of 50-340 GPa beyond the linear elasticity approximation, conventionally assumed in theoretical studies. We define the higher order elastic constants and present expressions for the long-wave acoustic modes Gruneisen parameters of a compressed hcp crystal. We obtain the second and third order elastic constants of the hcp Fe in the considered pressure interval, as well as its Gruneisen parameters for the high-symmetry directions. The latter are directly compared with the Gruneisen parameters derived from the volume dependences of the vibrational frequencies calculated in the quasiharmonic approximation. The obtained results are used for the stability analysis of the hcp phase of iron at high pressures.

  • 125.
    Lane, Nina J
    et al.
    Drexel University.
    Simak, Sergey
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics . Linköping University, The Institute of Technology.
    Mikhaylushkin, Arkady
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics . Linköping University, The Institute of Technology.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics . Linköping University, The Institute of Technology.
    Hultman, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Barsoum, Michel W
    Drexel University.
    First-principles study of dislocations in hcp metals through the investigation of the (11(2)over-bar1) twin boundary2011In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 84, no 18, p. 184101-Article in journal (Refereed)
    Abstract [en]

    Herein, we use first principles calculations to study the energy of the (11 (2) over bar1) twin boundary in Zr, Zn, Mg, Ti, and Be. This boundary is important for understanding the microyielding and damping of hexagonal close-packed metals. The (11 (2) over bar1) twin boundary is unique in that it is composed of-and can form by the glide of-basal dislocations nucleating at every c lattice parameter. The effect of the number of atoms between boundaries on the boundary energy, and the resulting lattice strains of the relaxed structures are quantified. It is shown that the energies obtained converge within 32-64 atoms/supercell. The structures with a higher second-order elastic constant term, c(44), also have higher boundary energies. It is further shown that the critical resolved shear stresses of the basal dislocations at 0 K, which make up the (11 (2) over bar1) twin, are so low as to be below the threshold of the first principles calculations.

  • 126.
    Laniel, Dominique
    et al.
    Univ Bayreuth, Germany.
    Bykov, Maxim
    Univ Bayreuth, Germany.
    Fedotenko, Timofey
    Univ Bayreuth, Germany.
    Ponomareva, Alena V.
    Natl Univ Sci and Technol MISIS, Russia.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Glazyrin, Konstantin
    DESY, Germany.
    Svitlyk, Volodymyr
    European Synchrotron Radiat Facil, France.
    Dubrovinsky, Leonid
    Univ Bayreuth, Germany.
    Dubrovinskaia, Natalia
    Univ Bayreuth, Germany.
    High Pressure Investigation of the S-N-2 System up to the Megabar Range: Synthesis and Characterization of the SN2 Solid2019In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 58, no 14, p. 9195-9204Article in journal (Refereed)
    Abstract [en]

    Sulfur and nitrogen represent one of the most studied inorganic binary systems at ambient pressure on account of their large wealth of metastable exotic ring-like compounds. Under high pressure conditions, however, their behavior is unknown. Here, sulfur and nitrogen were compressed in a diamond anvil cell up to about 120 GPa and laser-heated at regular pressure intervals in an attempt to stabilize novel sulfur nitrogen compounds. Above 64 GPa, an orthorhombic (space group Pnnm) SN2 compound was synthesized and characterized by single-crystal and powder X-ray diffraction as well as Raman spectroscopy. It is shown to adopt a CaCl2-type structure hence it is isostructural, isomassic, and isoelectronic to CaCl2-type SiO2 comprised of SN6 octahedra. Complementary theoretical calculations were performed to provide further insight into the physicochemical properties of SN2, notably its equation of state, the bonding type between its constitutive elements, and its electronic density of states. This new solid is shown to be metastable down to about 20 GPa, after which it spontaneously decomposes into S and N-2. This investigation shows that despite the many metastable S N compounds existing at ambient conditions, none of them are formed by pressure.

  • 127.
    Leonov, I.
    et al.
    University of Augsburg, Germany; National University of Science and Technology MISIS, Russia.
    Greenberg, E.
    Tel Aviv University, Israel; University of Chicago, IL USA.
    Belov, M. P.
    National University of Science and Technology MISIS, Russia.
    Rozenberg, G. Kh.
    Tel Aviv University, Israel.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Mott transition and magnetic collapse in iron-bearing compounds under high pressure2017In: High Pressure Research, ISSN 0895-7959, E-ISSN 1477-2299, Vol. 37, no 2, p. 96-118Article in journal (Refereed)
    Abstract [en]

    We discuss the electronic, magnetic, and related structural transitions in the iron-based Mott insulators under high pressures relevant to the Earths lower mantle conditions. The paper focuses on the above-mentioned topics based primarily on our theoretical analysis and various experimental studies employing synchrotron X-ray diffraction, Fe-57 Mossbauer spectroscopy, and electrical transport measurements. We review the main theoretical tools employed for the analysis of the properties of materials with strongly interacting electrons and discuss the problems of theoretical description of such systems. In particular, we discuss a state-of-the-art method for calculating the electronic structure of strongly correlated materials, the DFT + DMFT method, which merges standard band-structure techniques (DFT) with dynamical mean-field theory of correlated electrons (DMFT). We employ this method to study the pressure-induced magnetic collapse in Mott insulators, such as wustite (FeO), magnesiowustite (Fe1-xMgx)O (x=0.25 and 0.75) and goethite (FeOOH), and explore the consequences of the magnetic collapse for the electronic structure and phase stability of these materials. We show that the paramagnetic cubic B1-structured FeO and (Fe,Mg)O and distorted orthorhombic (Pnma) FeOOH exhibit upon compression a high-to low-spin (HS-LS) transition, which is accompanied by a simultaneous collapse of local moments. However, the HS-LS transition is found to have different consequences for the electronic properties of these compounds. For FeO and (Fe0.75Mg0.25)O, the transition is found to be accompanied by a Mott insulator-to-metal phase transition. In contrast to that, both (Fe0.25Mg0.75)O and FeOOH remain insulating up to the highest studied pressures, indicating that a Mott insulator to band insulator phase transition takes place. Our combined theoretical and experimental studies indicate a crossover between localized to itinerant moment behavior to accompany magnetic collapse of Fe ions.

  • 128.
    Leonov, I.
    et al.
    University of Augsburg, Germany; National University of Science and Technology MISIS, Russia.
    Ponomareva, A. V.
    National University of Science and Technology MISIS, Russia.
    Nazarov, R.
    Lawrence Livermore National Lab, CA 94551 USA.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Pressure-induced spin-state transition of iron in magnesiowustite (Fe,Mg)O2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, no 7, article id 075136Article in journal (Refereed)
    Abstract [en]

    We present a detailed theoretical study of the electronic, magnetic, and structural properties of magnesiowustite Fe-1 Mg-x(x) O with x in the range between 0 and 0.875 using a fully charge self-consistent implementation of the density functional theory plus dynamical mean-field theory method. In particular, we compute the electronic structure and phase stability of the rocksalt B1-structured (Fe,Mg) O at high pressures relevant for the Earths lower mantle. We find that upon compression paramagnetic (Fe,Mg) O exhibits a spin-state transition of Fe2+ ions from a high-spin to low-spin (HS-LS) state which is accompanied by a collapse of local magnetic moments. The HS-LS transition results in a substantial drop in the lattice volume by about 4%-8%, implying a complex interplay between electronic and lattice degrees of freedom. Our results reveal a strong sensitivity of the calculated transition pressure P-tr. upon addition of Mg. While, for Fe-rich magnesiowustite with Mg x amp;lt; 0.5, Ptr. is about 80 GPa, for Mg x = 0.75 it drops to 52 GPa, i. e., by 35%. This behavior is accompanied by a substantial change in the spin transition range from 50 to 140 GPa in FeO to 30 to 90 GPa for x = 0.75. In addition, the calculated bulk modulus (in the HS state) is found to increase by similar to 12% from 142 GPa in FeO to 159 GPa in (Fe,Mg) O with Mg x = 0.875. We find that the pressure-induced HS-LS transition has different consequences for the electronic properties of the Fe-rich and -poor (Fe,Mg) O. For the Fe-rich (Fe,Mg) O, the transition is found to be accompanied by a Mott insulator to a (semi) metal phase transition. In contrast to that, for x amp;gt; 0.25, (Fe,Mg) O remains insulating up to the highest studied pressures, implying a Mott-insulator to band-insulator phase transition at the HS-LS transformation.

  • 129.
    Leonov, I.
    et al.
    University of Augsburg, Germany; National University of Science and Technology MISIS, Russia.
    Pourovskii, L.
    National University of Science and Technology MISIS, Russia; University of Paris Saclay, France; Coll France, France.
    Georges, A.
    University of Paris Saclay, France; Coll France, France; University of Geneva, Switzerland.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. National University of Science and Technology MISIS, Russia.
    Magnetic collapse and the behavior of transition metal oxides at high pressure2016In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 94, no 15, p. 155135-Article in journal (Refereed)
    Abstract [en]

    We report a detail theoretical study of the electronic structure and phase stability of transition metal oxides MnO, FeO, CoO, and NiO in their paramagnetic cubic B1 structure by employing dynamical mean-field theory of correlated electrons combined with ab initio band-structure methods. Our calculations reveal that under pressure these materials exhibit a Mott insulator-metal transition (IMT) which is accompanied by a simultaneous collapse of local magnetic moments and lattice volume, implying a complex interplay between chemical bonding and electronic correlations. Moreover, our results for the transition pressure show a monotonous decrease from similar to 145 to 40 GPa, upon moving from MnO to CoO. In contrast to that, in NiO, magnetic collapse is found to occur at a remarkably higher pressure of similar to 429 GPa. We provide a unified picture of such a behavior and suggest that it is primarily a localized to itinerant moment behavior transition at the IMT that gives rise to magnetic collapse in transition metal oxides.

  • 130.
    Leonov, Ivan
    et al.
    Russian Acad Sci, Russia; Natl Univ Sci and Technol MISIS, Russia.
    Rozenberg, Gregory Kh
    Tel Aviv Univ, Israel.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Natl Univ Sci and Technol MISIS, Russia.
    Charge disproportionation and site-selective local magnetic moments in the post-perovskite-type Fe2O3 under ultra-high pressures2019In: NPJ COMPUTATIONAL MATERIALS, ISSN 2057-3960, Vol. 5, article id 90Article in journal (Refereed)
    Abstract [en]

    The archetypal 3d Mott insulator hematite, Fe2O3, is one of the basic oxide components playing an important role in mineralogy of Earths lower mantle. Its high pressure-temperature behavior, such as the electronic properties, equation of state, and phase stability is of fundamental importance for understanding the properties and evolution of the Earths interior. Here, we study the electronic structure, magnetic state, and lattice stability of Fe2O3 at ultra-high pressures using the density functional plus dynamical mean-field theory (DFT + DMFT) approach. In the vicinity of a Mott transition, Fe2O3 is found to exhibit a series of complex electronic, magnetic, and structural transformations. In particular, it makes a phase transition to a metal with a post-perovskite crystal structure and site-selective local moments upon compression above 75 GPa. We show that the site-selective phase transition is accompanied by a charge disproportionation of Fe ions, with Fe-3 +/-delta and delta similar to 0.05-0.09, implying a complex interplay between electronic correlations and the lattice. Our results suggest that site-selective local moments in Fe2O3 persist up to ultra-high pressures of similar to 200-250 GPa, i.e., sufficiently above the core-mantle boundary. The latter can have important consequences for understanding of the velocity and density anomalies in the Earths lower mantle.

  • 131.
    Lind, Hans
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Forsén, Rikard
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics.
    Alling, Björn
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Ghafoor, Naureen
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Tasnadi, Ferenc
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Johansson, M P
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, The Institute of Technology.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Odén, Magnus
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, The Institute of Technology.
    Improving thermal stability of hard coating films via a concept of multicomponent alloying2011In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 99, no 9, p. 091903-Article in journal (Refereed)
    Abstract [en]

    We propose a design route for the next generation of nitride alloys via a concept of multicomponent alloying based on self-organization on the nanoscale via a formation of metastable intermediate products during the spinodal decomposition. We predict theoretically and demonstrate experimentally that quasi-ternary (TiCrAl)N alloys decompose spinodally into (TiCr)N and (CrAl)N-rich nanometer sized regions. The spinodal decomposition results in age hardening, while the presence of Cr within the AlN phase delays the formation of a detrimental wurtzite phase leading to a substantial improvement of thermal stability compared to the quasi-binary (TiAl)N or (CrAl)N alloys.

  • 132.
    Lind, Hans
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Pilemalm, Robert
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, The Institute of Technology.
    Rogström, Lina
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, The Institute of Technology.
    Tasnadi, Ferenc
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Ghafoor, Naureen
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, The Institute of Technology.
    Forsén, Rikard
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, The Institute of Technology.
    Johnson, Lars
    Sandvik Coromant, Stockholm, Sweden.
    Jöesaar, Mats
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, The Institute of Technology. SECO Tools AB, Fagersta, Sweden.
    Odén, Magnus
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, The Institute of Technology.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    High temperature phase decomposition in TixZryAlzN2014In: AIP Advances, ISSN 2158-3226, E-ISSN 2158-3226, Vol. 4, no 12, p. 127147-1-127147-9Article in journal (Refereed)
    Abstract [en]

    Through a combination of theoretical and experimental observations we study the high temperature decomposition behavior of c-(TixZryAlzN) alloys. We show that for most concentrations the high formation energy of (ZrAl)N causes a strong tendency for spinodal decomposition between ZrN and AlN while other decompositions tendencies are suppressed. In addition we observe that entropic  effects due to configurational disorder favor a formation of a stable Zr-rich (TiZr)N phase with increasing temperature. Our calculations also predict that at high temperatures a Zr rich (TiZrAl)N disordered phase should become more resistant against the spinodal decomposition despite its high and positive formation energy due to the specific topology of the free energy surface at the relevant concentrations. Our experimental observations confirm this prediction by showing strong tendency towards decomposition in a Zr-poor sample while a Zr-rich alloy shows a greatly reduced decomposition rate, which is mostly attributable to binodal decomposition processes. This result highlights the importance of considering the second derivative of the free energy, in addition to its absolute value in predicting decomposition trends of thermodynamically unstable alloys.

  • 133.
    Lind, Hans
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Tasnadi, Ferenc
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Systematic theoretical search for alloys with increased thermal stability for advanced hard coatings applications2013In: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 15Article in journal (Refereed)
    Abstract [en]

    State-of-the-art alloys for hard coating applications, such as TiAlN, are known to suffer from decreased hardness during heat treatment in excess of 900 °C due to the formation of detrimental wurtzite AlN phases. Recent research has shown that multicomponent alloying with additional transition metals (TMs) such as Cr can shift the onset of the phase transformations to higher temperatures, but a search for new alloys is generally time-consuming due to the large number of processes that influence material properties along with the large number of alloy compositions that have to be synthesized. To overcome this difficulty we carry out systematic first-principles calculations aimed at finding potential new multicomponent TM aluminum nitride alloys for advanced hard coating applications. We direct our search towards a specific property, the thermal stability of the coating. In particular, we concentrate on the thermodynamic stability of the cubic B1 TM–Al–N phase relative to the wurtzite phase, and choose the enthalpy difference between them as our search descriptor. We perform ab initio calculations for all TMs, considered as impurities in AlN, and identify the most promising candidates that may improve the thermal stability. We present arguments that these elements should be targeted in future in-depth studies, theoretical, as well as experimental.

  • 134.
    Lind, Hans
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Tasnádi, Ferenc
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Abrikosov, Igor A.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Ti and Cr impurities in cubic and hexagonal AlNManuscript (preprint) (Other academic)
    Abstract [en]

    AlN is a wide band gap semiconductor that is used in many fields, e.g. as electronic material, for piezoelectric applications but also as a component material in high performance hard coating alloys. The stable structure under ambient conditions is a hexagonal wurtzite structure, but it has also been observed in the tetrahedrally bonded cubic zinc-blende structure as well as cubic rock-salt phases that become stable at high pressure. The metastable rock-salt phase of AlN also forms during decomposition processes in hard-coating alloys such as (TiAl)N, (CrAl)N and (TiCrAl)N. Even though thermodynamically unstable, one can expect some amount of Ti and Cr to be present in the c-AlN phase during the decomposition. Still, little study has been done for the dilute (TMAl)N alloys with cubic B1 crystal structure. We study the electronic structure of Ti and Cr impurities in B1 AlN. Because of the limitations of standard local and semi-local approximations within the density functional theory (DFT) in the treatment of wide band gap semiconductors, as well as conventional hybrid functionals for systems consisting of correlated localized and delocalized orbitals, we apply the mHSE+Vw method, which has been developed specifically to dealing with these kind of problems. Simulations are done by means of the supercell technique with single impurities, as well as for the impurity pairs. The effects of different atomic configurations of the TM-impurities on phase stability and magnetic properties of the cubic B1 AlN is studied and compared to the those in hexagonal B4 structures. Our results underline the importance of correlation and magnetic effects for the description of properties of cubic AlN doped with Ti and Cr.

  • 135.
    Lindmaa, Alexander
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Lizarraga, R
    University of Austral Chile, Chile.
    Holmstrom, E
    University of Austral Chile, Chile.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Alling, Björn
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Exchange interactions in paramagnetic amorphous and disordered crystalline CrN-based systems2013In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 88, no 5Article in journal (Refereed)
    Abstract [en]

    We present a first principles supercell methodology for the calculation of exchange interactions of magnetic materials with arbitrary degrees of structural and chemical disorder in their high temperature paramagnetic state. It is based on a projection of the total magnetic energy of the system onto local pair clusters, allowing the interactions to vary independently as a response to their local environments. We demonstrate our method by deriving the distance dependent exchange interactions in vibrating crystalline CrN, a Ti0.5Cr0.5N solid solution as well as in amorphous CrN. Our method reveals strong local environment effects in all three systems. In the amorphous case we use the full set of exchange interactions in a search for the noncollinear magnetic ground state.

  • 136.
    Liot, Francois
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics . Linköping University, The Institute of Technology.
    Simak, Sergey
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics . Linköping University, The Institute of Technology.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics . Linköping University, The Institute of Technology.
    Static Ionic Displacements in Fe-Ni Alloys from First-Principles2006In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 99, p. 08P906-Article in journal (Refereed)
    Abstract [en]

    Static local displacements of ions in disordered face-centered cubic Fe50Ni50 alloy are studied from first principles in the framework of the density functional theory. The disordered alloy is modeled using a 64 atom supercell constructed as a special quasirandom structure. Fully relaxed atomic positions inside the supercell are calculated by means of projected augmented wave method as implemented in Vienna ab initio simulation package. According to our calculation, the relative changes of mean nearest neighbor interatomic distances due to local lattice relaxations are relatively small (0.6%), in agreement with experiment. At the same time, we predict that for all types of pairs, Fe–Fe, Fe–Ni, and Ni–Ni, the dispersion of the nearest neighbor interatomic distances is rather large, and the individual changes of distances between certain pairs of atoms due to local lattice relaxations can be one order of magnitude larger than the mean values for the corresponding pair of atoms

  • 137.
    Liot, Francois
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics . Linköping University, The Institute of Technology.
    Abrikosov , Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics . Linköping University, The Institute of Technology.
    Local magnetovolume effects in Fe65Ni35 alloys2009In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 79, no 1, p. 014202-Article in journal (Refereed)
    Abstract [en]

    A systematic ab initio study of static ionic displacements in a face-centered-cubic Fe65Ni35 alloy has been carried out. Theoretical results for magnitudes of average Fe-Fe, Fe-Ni, and Ni-Ni < 110 > bond vectors agree well with experimental measurements. In addition, we have observed that in collinear ferrimagnetic states, iron-iron nearest-neighbor pairs with antiparallel local magnetic moments are shorter on average than those with parallel moments. Furthermore, having considered different states (ferromagnetic, nonmagnetic, and collinear ferrimagnetic states) for the same lattice spacing, we have shown that the magnetic structure strongly influences local geometrical properties of the alloy. For example, a transition from a ferromagnetic state to a collinear ferrimagnetic state induces a significant contraction of the volume associated with an iron site where the moment flips. A model system based on a Hamiltonian written as the sum of Lennard-Jones energies and a classical Heisenberg Hamiltonian has been introduced. It yields structural properties which are qualitatively similar to those obtained ab initio. We have found that some of the phenomena can be classified as magnetovolume effects.

  • 138.
    Magnuson, Martin
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics.
    Mattesini, Maurizio
    University Complutense Madrid.
    Höglund, Carina
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Birch, Jens
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Hultman, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Electronic structure investigation of the cubic inverse perovskite Sc3AlN2008In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 78, no 23, p. 235102-Article in journal (Refereed)
    Abstract [en]

    The electronic structure and chemical bonding of the recently discovered inverse perovskite Sc3AlN, in comparison to those of ScN and Sc metal, have been investigated by bulk-sensitive soft-x-ray emission spectroscopy. The measured Sc L, N K, Al L-1, and Al L-2,L-3 emission spectra are compared with calculated spectra using first-principles density-functional theory including dipole transition-matrix elements. The main Sc 3d-N 2p and Sc 3d-Al 3p chemical bond regions are identified at -4 and -1.4 eV below the Fermi level, respectively. A strongly modified spectral shape of 3s states in the Al L-2,L-3 emission from Sc3AlN in comparison to that for pure Al metal is found, which reflects the Sc 3d-Al 3p hybridization observed in the Al L-1 emission. The differences between the electronic structures of Sc3AlN, ScN, and Sc metal are discussed in relation to the change in the conductivity and elastic properties.

  • 139.
    Marten, Tobias
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics . Linköping University, The Institute of Technology.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics . Linköping University, The Institute of Technology.
    Olovsson, W
    Kyoto University.
    Johansson, B
    Uppsala University.
    Cole, R J
    University Edinburgh.
    Beamson, G
    STFC Daresbury Laboratory, Warrington.
    Haines, S R
    University of Liverpool.
    Weightman, P
    University of Liverpool.
    Suppression of disorder broadening of core-level photoelectron lines in CuAu alloys by inhomogeneous lattice distortion2009In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 79, no 1, p. 012201-Article in journal (Refereed)
    Abstract [en]

    Disorder broadening of core-level binding energies is a general effect observed in random alloys, and identifies an opportunity for studying specific local environments experimentally. Here we study it in an archetypical system: face-centered-cubic Cu50Au50. While the disorder broadening is clearly detectable at Au, at Cu it is below the detection limit. We supplement experiments by a theoretical study where we model the alloy by a large supercell constructed as a special quasirandom structure and calculate binding-energy shifts at all sites in the supercell. Theory shows that the suppression of the disorder broadening at Cu results from a delicate balance between the influence of local chemical environment and inhomogeneous lattice distortions on the site-resolved core-level shifts. Surprisingly, even larger relaxation-induced shifts are observed at Au sites.

  • 140.
    Marten, Tobias
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Alling, Björn
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Isaev, Eyvas
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Lind, Hans
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Tasnadi, Ferenc
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Hultman, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    First-principles study of the SiNx/TiN(001) interface2012In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 85, no 10, p. 104106-Article in journal (Refereed)
    Abstract [en]

    The structure of the SiNx tissue phase in superhard TiN/SiNx nanocomposites has been debated in the literature. We present a theoretical investigation of the possibility of crystalline and coherent ( 001) interfaces that satisfies the two necessary criteria, stability with respect to lattice vibrations as well as to variations in stoichiometry. It is found that one monolayer of Si tetrahedrally coordinated by N in a B3-like geometry embedded between B1-TiN( 001) surfaces is both dynamically stable and thermodynamically stable with respect to vacancy formation. However, with increasing layer thickness the B3-type structure becomes unstable with respect to Si vacancy formation. Instead we suggest that a tetragonal D0(22)-like order of Si vacancies can stabilize the interface. These structures are in line with the experimental findings of the crystalline tissue phase which has coherent interfaces with TiN.

  • 141.
    Marten, Tobias
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics . Linköping University, The Institute of Technology.
    Hellman, Olle
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics . Linköping University, The Institute of Technology.
    Ruban, Andrei V.
    Department of Materials Science and Engineering Royal Institute of Technology, Stockholm.
    Olovsson, Weine
    Department of Materials Science and Engineering, Kyoto University, Kyoto 606-8501, Japan.
    Kramer, Charlotte
    Department of Physics and Nanotechnology Aalborg University, Aalborg, Denmark.
    Godowski, Jan P.
    Institute of Experimental Physics, University of Wroclaw, 50-204 Wroclaw, Poland.
    Bech, Lone
    Department of Physics and Nanotechnology, Aalborg University, DK-9220 Aalborg East, Denmark.
    Li, Zheshen
    Institute of Storage Ring Facilities, University of Aarhus, DK-8000 Aarhus, Denmark.
    Onsgaard, Jens
    Department of Physics and Nanotechnology, Aalborg University, DK-9220 Aalborg East, Denmark.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics . Linköping University, The Institute of Technology.
    Double-segregation effect in AgxPd1−x /Ru(0001) thin film nanostructures2008In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 77, p. 125406-1-125406-7Article in journal (Refereed)
    Abstract [en]

    We study the structural properties of ultrathin AgxPd1−x films on top of a Ru(0001) substrate. Effective interatomic interactions, obtained from first-principles calculations, have been used in Monte Carlo simulations to derive the distribution of the alloy components in a four-monolayer (4-ML) Ag-Pd film. Though Ag-Pd alloys show complete solubility in the bulk, the thin film geometry leads to a pronounced segregation between Ag and Pd atoms with a strong preference of Ag atoms toward the surface and Pd atoms toward the interface. The theoretical prediction of this double-segregation effect is strongly supported by photoelectron spectroscopy experiments carried out for 4-ML thin films. We also show, in an additional experiment, that even in the case where initially 1 ML Ag is buried under 6 ML Pd, the whole Ag ML segregates to the surface.

  • 142.
    Marten, Tobias
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics . Linköping University, The Institute of Technology.
    Isaev, Eyvas
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics .
    Alling, Björn
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics . Linköping University, The Institute of Technology.
    Hultman, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics . Linköping University, The Institute of Technology.
    Single-monolayer SiNx embedded in TiN: A first-principles study2010In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 81, no 21, p. 212102-Article in journal (Refereed)
    Abstract [en]

    The dynamical and thermodynamic stability of a single monolayer of SiNx sandwiched isostructurally between B1-TiN(001) and (111) oriented slabs are investigated by means of density functional theory. Possible dynamical stabilization of the (001) interface, by distortion of the Si-N bonds, is considered and found to almost, but not completely, remove the phonon instabilities. The (111) interface on the other hand is found to be dynamically stable. We furthermore relax the stoichiometry degree of freedom by allowing for Si vacancies in the lattice and show that the ideal 1:1 SiN stoichiometry in both interfaces are thermodynamically unstable with respect to Si vacancy formation regardless if the system is grown under nitrogen-rich or nitrogen-poor conditions, and therefore ruling out its relevance for performance of real materials.

  • 143.
    Marten, Tobias
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics .
    Simak, Sergey
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics .
    Olovsson, Weine
    Department of Physics Uppsala University.
    Abrikosov, Igor
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics .
    Ab initio study of disorder broadening of core photoemission spectra in random Cu-Pd and Ag-Pd alloys2005In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 72, no 5Article in journal (Refereed)
    Abstract [en]

    A first-principles study of the effect of local environment on the electronic structure of random face-centered cubic Ag-Pd and Cu-Pd alloys is presented. The core-level shift for each atom in the equiatomic alloys is calculated and compared to experimental data. It is shown how the initial-state and final-state distributions contribute to the total broadening. We find that the initial-state and the final-state contributions together increase the broadening for the investigated core levels in Cu and Ag, whereas they cancel each other to a large degree for Pd. We also demonstrated how local lattice relaxations influence the binding energy shift. We find that relaxation does not influence the average shift, though it is able to affect the broadening of the simulated x-ray photoelectron spectroscopy spectra. © 2005 The American Physical Society.

  • 144.
    Mattesini, Maurizio
    et al.
    Universidad Complutense de Madrid.
    Magnuson, Martin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics.
    Tasnádi, Ferenc
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Höglund, Carina
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Abrikosov, Igor A.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Hultman, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Elastic properties and electrostructural correlations in ternary scandium-based cubic inverse perovskites: A first-principles study2009In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 79, no 125122Article in journal (Refereed)
    Abstract [en]

    Wehave performed ab initio calculations for the cubic inverse-perovskite Sc3EN(E=Al,Ga,In) systems to study their electronic band-structures and elastic properties.In this study, we used the accurate augmented plane waveplus local orbital method to find the equilibrium structural parametersand to compute the full elastic tensors. The obtained single-crystalelastic constants were used to quantify the stiffness of theSc-based ternary nitrides and to appraise their mechanical stability. Thesite-projected density of states, Fermi surfaces, and the charge-density plotshave also been used to analyze the chemical bonding betweenthe Sc6N cluster and the surrounding metallic lattice of eitherAl, Ga, or In atoms. Our calculations show that Sc3GaNhas the largest covalent Sc-N bonding-type character with the highestYoung, shear, and bulk moduli. Compared with the other twoisoelectronic systems, it also behaves as the most brittle materialwith a relatively large elastic anisotropy.

  • 145.
    Mikhaylushkin, Arkady
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics . Linköping University, The Institute of Technology.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics . Linköping University, The Institute of Technology.
    Belonoshko, A B
    Royal Institute of Technology.
    Johansson, B
    Royal Institute of Technology.
    Simak , Sergey
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics . Linköping University, The Institute of Technology.
    Instability of the body-centered tetragonal phase of iron under extreme conditions2009In: PHYSICAL REVIEW B, ISSN 1098-0121 , Vol. 79, no 13, p. 132106-Article in journal (Refereed)
    Abstract [en]

    The influence of the tetragonal and orthorhombic axial distortions on the body-centered cubic (bcc) phase of Fe at extreme conditions has been studied by means of first-principles calculations. We unambigiously demonstrate that the energy minimum corresponding to the body-centered tetragonal (bct) (c/a approximate to 0.9) structure, previously found in Fe upon the axial tetragonal distortion of the bcc phase along the Bains path under compression at zero temperature, is an artifact of the structural constraint. When the bcc structure is examined using the orthorhombic distortion involving the tetragonal distortion as a particular case, the bct (c/a approximate to 0.9) structural framework represents a saddle point between two mirrored face-centered cubic minima rather than a local minimum. Therefore we conclude that there is no ground to emphasize on possible thermal stabilization of the bct structure with a particular c/a ratio apart from the whole family of structures obtained by tetragonal, orthorhombic, or another type of axial distortions.

  • 146.
    Mikhaylushkin, Arkady
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics . Linköping University, The Institute of Technology.
    Höglund, Carina
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Birch, Jens
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Czigany, Zs
    Hungarian Acadamy of Science.
    Hultman, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Simak, Sergey
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics . Linköping University, The Institute of Technology.
    Alling, Björn
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics . Linköping University, The Institute of Technology.
    Tasnadi, Ferenc
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics . Linköping University, The Institute of Technology.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics . Linköping University, The Institute of Technology.
    Stability of the ternary perovskites Sc3EN (E=B,Al,Ga,In) from first principles2009In: PHYSICAL REVIEW B, ISSN 1098-0121, Vol. 79, no 13, p. 134107-Article in journal (Refereed)
    Abstract [en]

    Mechanical and thermodynamic stability of the isoelectronic ternary inverse perovskites Sc3EN (E=B,Al,Ga,In) has been studied from first principles. We confirm stability of recently synthesized cubic phases Sc3AlN and Sc3InN, and predict the stability of cubic Sc3GaN and a triclinic phase aP20-Sc3BN. Substantial phonon softening in Sc3AlN and Sc3GaN is observed indicating a possibility that structural defects could form readily. In accord, our experiments show that magnetron sputter deposited films contain regions with high density of nonperiodic stacking faults along the < 111 > growth direction. We suggest that defect-free crystals may exhibit anomalies in the carrier properties, promising for electronic applications.

  • 147.
    Mikhaylushkin, Arkady
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Simak, Sergey
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Voyage to the Earth's Deep Interior2008In: NCS News, no 3, p. 3-5Article in journal (Other (popular science, discussion, etc.))
  • 148.
    Mikhaylushkin, Arkady
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics .
    Simak, Sergey
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics .
    Dubrovinsky, L.
    Bayersches Geoinstitut Universitet Bayreuth.
    Dubrovinskaia, N.
    Bayersches Geoinstitut Universitet Bayreuth.
    Johansson, B.
    Department of Material Science and Engineering Royal Institute of Technology.
    Abrikosov, Igor
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics .
    Iron compressed and heated to extreme conditions2008In: American Physical Society March Meeting 2008,2008, 2008Conference paper (Refereed)
  • 149.
    Mikhaylushkin, Arkady
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics .
    Simak, Sergey
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics .
    Dubrovinsky, Leonid
    Bayerisches Geoinstitut Universitat Bayreuth, D-95440 Bayreuth, Germany.
    Dubrovinskaia,, N.
    Mineralogisches Institut Universita¨t Heidelberg, 69120 Heidelberg, Germany.
    Johansson,, Börje
    Department of Physics Uppsala University, Uppsala.
    Abrikosov, Igor
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics .
    Pure Iron Compressed and Heated to Extreme Conditions2007In: Physical review letters / publ. by the American Physical Society, Vol. 99, p. 165505-1-165505-4Article in journal (Refereed)
  • 150.
    Mondal, Swastik
    et al.
    Laboratory of Crystallography, University of Bayreuth, Germany.
    van Smaalen, Sander
    Laboratory of Crystallography, University of Bayreuth, Germany.
    Schoenleber, Andreas
    Laboratory of Crystallography, University of Bayreuth, Germany.
    Filinchuk, Yaroslav
    Swiss-Norwegian Beam Line, ESRF, Grenoble, France.
    Chernyshov, Dmitry
    Swiss-Norwegian Beam Line, ESRF, Grenoble, France.
    Simak, Sergey
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics . Linköping University, The Institute of Technology.
    Mikhaylushkin, Arkady
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics . Linköping University, The Institute of Technology.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics . Linköping University, The Institute of Technology.
    Zarechnaya, Evgeniya
    Bayerisches Geoinstitut, University of Bayreuth, Germany.
    Dubrovinsky, Leonid
    Bayerisches Geoinstitut, University of Bayreuth, Germany.
    Dubrovinskaia, Natalia
    Laboratory of Crystallography, University of Bayreuth, Germany.
    Electron-Deficient and Polycenter Bonds in the High-Pressure gamma-B-28 Phase of Boron2011In: PHYSICAL REVIEW LETTERS, ISSN 0031-9007, Vol. 106, no 21, p. 215502-Article in journal (Refereed)
    Abstract [en]

    The peculiar bonding situation in gamma boron is characterized on the basis of an experimental electron-density distribution which is obtained by multipole refinement against low-temperature single-crystal x-ray diffraction data. A topological analysis of the electron-density distribution reveals one-electron-two-center bonds connecting neighboring icosahedral B-12 clusters. A unique polar-covalent two-electron-three-center bond between a pair of atoms of an icosahedral cluster and one atom of the interstitial B-2 dumbbell explains the observed charge separation in this high-pressure high-temperature polymorph of boron.

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