K. Schwarz

Vienna University of Technology, Wien, Vienna, Austria

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Publications (259)671.27 Total impact

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    Fabien Tran · Peter Blaha · Karlheinz Schwarz
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    ABSTRACT: The Becke–Roussel (BR) potential [Phys. Rev. A 1989, 39, 3761] was proposed as an approximation to the Slater potential, which is the Coulomb potential generated by the exact exchange hole. In the present work, a detailed comparison between the Slater and BR potentials in solids is presented. It is shown that the two potentials usually lead to very similar results for the electronic structure; however, in a few cases, e.g., Si, Ge, or strongly correlated systems like NiO, the fundamental band gap or magnetic properties can differ markedly. Such differences should not be neglected when the computationally expensive Slater potential is replaced by the cheap semilocal BR potential in approximations to the exact-exchange Kohn–Sham potential, such as the one proposed by Becke and Johnson [J. Chem. Phys. 2006, 124, 221101].
    Preview · Article · Aug 2015 · Journal of Chemical Theory and Computation
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    Full-text · Dataset · Jan 2015
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    Full-text · Dataset · Jan 2015
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    ABSTRACT: We investigate theoretically the site occupancy of Al3+ in the fast-ion-conducting cubic-garnet Li7–3xAl3+xLa3Zr2O12 (Ia-3d) using density functional theory. By comparing calculated and measured 27Al NMR chemical shifts an analysis shows that Al3+ prefers the tetrahedrally coordinated 24d site and a distorted 4-fold coordinated 96h site. The site energies for Al3+ ions, which are slightly displaced from the exact crystallographic sites (i.e., 24d and 96h), are similar leading to a distribution of slightly different local oxygen coordination environments. Thus, broad 27Al NMR resonances result reflecting the distribution of different isotropic chemical shifts and quadrupole coupling constants. From an energetic point of view, there is evidence that Al3+ could also occupy the 48g site with its almost regular octahedral coordination sphere. Although this has been reported by neutron powder diffraction, the NMR chemical shift calculated for such an Al3+ site has not been observed experimentally.
    Full-text · Article · Apr 2014 · Chemistry of Materials
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    ABSTRACT: We investigate theoretically the site occupancy of Al 3+ in the fast-ion-conducting cubic-garnet Li 7−3x Al 3+ x La 3 Zr 2 O 12 (Ia-3d) using density functional theory. By comparing calculated and measured 27 Al NMR chemical shifts an analysis shows that Al 3+ prefers the tetrahedrally coordinated 24d site and a distorted 4-fold coordinated 96h site. The site energies for Al 3+ ions, which are slightly displaced from the exact crystallographic sites (i.e., 24d and 96h), are similar leading to a distribution of slightly different local oxygen coordination environments. Thus, broad 27 Al NMR resonances result reflecting the distribution of different isotropic chemical shifts and quadrupole coupling constants. From an energetic point of view, there is evidence that Al 3+ could also occupy the 48g site with its almost regular octahedral coordination sphere. Although this has been reported by neutron powder diffraction, the NMR chemical shift calculated for such an Al 3+ site has not been observed experimentally.
    Full-text · Dataset · Mar 2014
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    Full-text · Dataset · Feb 2014
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    ABSTRACT: Multiferroic materials, in which ferroelectric and magnetic ordering coexist, are of fundamental interest for the development of multi-state memory devices that allow for electrical writing and non-destructive magnetic readout operation. The great challenge is to create multiferroic materials that operate at room temperature and have a large ferroelectric polarization P. Cupric oxide, CuO, is promising because it exhibits a significant polarization, that is, P~0.1 μC cm(-2), for a spin-spiral multiferroic. Unfortunately, CuO is only ferroelectric in a temperature range of 20 K, from 210 to 230 K. Here, by using a combination of density functional theory and Monte Carlo calculations, we establish that pressure-driven phase competition induces a giant stabilization of the multiferroic phase of CuO, which at 20-40 GPa becomes stable in a domain larger than 300 K, from 0 to T>300 K. Thus, under high pressure, CuO is predicted to be a room-temperature multiferroic with large polarization.
    Full-text · Article · Sep 2013 · Nature Communications
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    ABSTRACT: Multiferroic materials, in which ferroelectric and magnetic ordering coexist, are of fundamental interest for the development of multi-state memory devices that allow for electrical writing and non-destructive magnetic read-out operation. The great challenge is to create multiferroic materials that operate at room-temperature and have a large ferroelectric polarization P. Cupric oxide, CuO, is promising because of its large P ~ 10^{2} {\mu}C.m^{-2}, but is unfortunately only multiferroic in a temperature range of 20 K, from 210 to 230 K. Here, using a combination of density functional theory and Monte Carlo calculations, we establish that pressure-driven phase competition induces a giant stabilization of the multiferroic phase of CuO, which at 20-40 GPa becomes stable in a domain larger than 300 K, from 0 to T > 300 K. Thus, under high-pressure, CuO is predicted to be a room-temperature multiferroic with large polarization.
    Full-text · Article · Sep 2013
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    ABSTRACT: Cited By (since 1996): 7, Export Date: 28 May 2012, Source: Scopus, Art. No.: 172401
    No preview · Article · Apr 2013 · Physical Review B
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    Full-text · Dataset · Mar 2013
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    Xavier Rocquefelte · Karlheinz Schwarz · Peter Blaha
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    ABSTRACT: It remains a challenge to understand the unconventional mechanisms that cause high-T(C) superconductivity in cuprate superconductors, high-T(C) multiferroicity in CuO, or low-dimensional magnetism in the spin-Peierls transition compounds such as CuGeO(3). A common feature of all these copper oxide compounds (containing Cu(2+) ions) is the presence of large magnetic superexchange interactions J. It is a general strategy to apply chemical and/or physical pressure in order to tune these exotic properties. Here we show theoretically, for the first time, the impact of physical pressure on J on CuO, for which we predict a strong enhancement of the low-dimensionality of the magnetic interactions and the spin-frustration at high-pressures. Such modifications are expected to strongly influence the multiferroic properties of CuO. We finally demonstrate that PBE0 hybrid DFT calculations provide reliable J values for a wide range of copper(II) oxides compounds, i.e. CuGeO(3), BaCu(2)Si(2)O(7), BaCu(2)Ge(2)O(7), and La(2)CuO(4.).
    Preview · Article · Oct 2012 · Scientific Reports
  • Hans Peter Koch · Robert Laskowski · Peter Blaha · Karlheinz Schwarz
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    ABSTRACT: The adsorption of small Aun (n=2–4) clusters on the h-BN/Rh(111) nanomesh is studied by means of density functional theory calculations. We demonstrate that for these small gold clusters a linear geometry is most stable, where all Au atoms bind to underlying B atoms in the pores of the 13×12 h-BN/Rh(111) nanomesh. However, other geometries have similar adsorption energies of more than 2 eV/atom. All Au atoms in these clusters are still negatively charged and thus might be catalytically active. Their partial density of states are significantly narrower and at smaller binding energies as compared to a Au(111) surface.
    No preview · Article · Oct 2012 · Physical review. B, Condensed matter
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    Evgeniya Kabliman · Andrei V. Ruban · Peter Blaha · Oleg Peil · Karlheinz Schwarz
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    ABSTRACT: The site occupation of binary Fe-Cr, Co-Cr, Re-W and Fe-V sigma phases is studied in the present work with a first-principles-based single-site mean field theory. We show that the alloy components in these systems exhibit similar site preferences except for the Re-W system, where the occupation of two sites is reversed in agreement with previously published works. In case of the FeV sigma phase, for which the size mismatch between the alloy components is large, we also include into our consideration the effect of local lattice relaxations. The obtained results are found in good agreement with the experimental data and previous theoretical studies.
    Full-text · Article · Sep 2012 · Applied Sciences
  • V.l.sliwko · P.blaha · P.mohn · K.schwarz
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    ABSTRACT: We have performed Augmented Spherical Wave (ASW) calculations on bcc Mn and confirmed previous results by Moruzzi and Marcus who reported a ferrimagnetic phase. Independent computations employing the full-potential linearized-augmented-plane-wave (LAPW) method led to similar results. Our ASW results yield the total energy and the magnetic moments as a function of volume assuming different (ferro-, ferri-, antiferro-and non-magnetic) bcc related structures with type I, II, and III spin alignments. We relate the relative stability of various phases to band gaps that open at the Fermi energy for certain volumes. The LAPW symmetry-decomposed partial charges allow to analyze the binding mechanism.
    No preview · Article · Jan 2012 · International Journal of Modern Physics B
  • E.hoffmann · H.herper · P.entel · P.mohn · K.schwarz
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    ABSTRACT: Fixed-spin-moment band-structure calculations of ordered fcc Fe3Ni reveal Fermisurface nesting, which can give rise to a Kohn-like anomaly. This nesting behaviour is very similar to what has recently been seen in nonmagnetic NixAl1–x.1 Using the method of Varma and Weber2 we discuss the renormalized phonon spectrum of Fe3Ni and investigate how the phonon softening and the martensitic transformation depend on the Fermi-surface nesting.
    No preview · Article · Jan 2012 · International Journal of Modern Physics B
  • P.mohn · K.schwarz
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    ABSTRACT: Based on the spin-density functional theory we discuss the essential mechanism of spin-split itinerant electrons which cause the formation of spin-magnetic moments in a solid. The success and the difficulties of the Stoner model of itinerant magnetism is shown for hcp Co. The FSM (fixed spin moment) method allows us to compute the total energy as a function of volume and magnetic moment, E(M, V). These energy surfaces contain the crucial information about magneto-volume instabilities and related phenomena. At finite temperatures collective phenomena such as spin fluctuations are important which can be treated with a Landau—Ginzburg formalism. Results are given for the finite temperature properties of the strongly enhanced Pauli paramagnet fcc Pd and the metamagnetic system YCo2.
    No preview · Article · Jan 2012 · International Journal of Modern Physics B
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    ABSTRACT: We have studied the angular-dependent de Haas-van Alphen oscillations of LaRu2P2 using magnetic torque in pulsed magnetic fields up to 60 T. The observed oscillation frequencies are in excellent agreement with the geometry of the calculated Fermi surface. The temperature dependence of the oscillation amplitudes reveals effective masses m*(α)=0.71 and m*(β)=0.99 me, which are enhanced over the calculated band mass by λcyc of 0.8. We find a similar enhancement of λγ≈1 in comparing the measured electronic specific heat (γ=11.5 mJ/mol K2) with the total density of states from band-structure calculations. Remarkably, very similar mass enhancements have been reported in other pnictides, LaFe2P2, LaFePO (Tc≈4 K), and LaRuPO, independent of whether they are superconducting or not. This is contrary to the common perceptions that the normal-state quasiparticle renormalizations reflect the strength of the superconducting pairing mechanism and leads to new questions about pairing in isostructural and isoelectronic Ru- and Fe-pnictide superconductors.
    Full-text · Article · Dec 2011 · Physical review. B, Condensed matter
  • Hans Peter Koch · Robert Laskowski · Peter Blaha · Karlheinz Schwarz
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    ABSTRACT: We present density functional calculations of the adsorption of a single Au atom on the h-BN/Rh(111) nanomesh and compare it to Au adsorption on a pure h-BN surface. While Au binds only weakly to pure h-BN (similar to graphene) or to BN at the “wires” of the nanomesh, the subsurface Rh atoms in the “pores” of the nanomesh modify the electronic structure of h-BN considerably and Au adsorbs strongly on top of the B atoms. A large outward relaxation of the B atom accompanies the strong covalent interaction and, in addition, the Au atoms are significantly charged. The results provide a first explanation of the ability of the h-BN nanomesh to trap small metal clusters in its pores.
    No preview · Article · Dec 2011 · Physical review. B, Condensed matter
  • Xavier Rocquefelte · Karlheinz Schwarz · Peter Blaha
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    ABSTRACT: A Comment on the Letter by Gianluca Giovannetti et al., Phys. Rev. Lett. 106, 026401 (2011). The authors of the Letter offer a Reply.
    No preview · Article · Dec 2011 · Physical Review Letters
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    ABSTRACT: Configurational thermodynamics of the Fe-Cr sigma phase is investigated on the basis of an Ising-type configurational Hamiltonian and a single-site mean-field model for the free energy. The parameters of the statistical models are obtained from efficient first-principles calculations using different computational techniques. We demonstrate that the effective pair and multisite interactions in the σ phase are relatively small, which allows using a simplified model for distributing Fe and Cr atoms among sublattices. We also show that this system exhibits a nontrivial magnetic behavior at high temperatures, which affects the site occupation by Fe and Cr atoms. The structural variation (volume and c/a) that might be present due to neutron irradiation and thermal expansion can lead to an additional atomic redistribution.
    Full-text · Article · Nov 2011 · Physical Review B

Publication Stats

12k Citations
671.27 Total Impact Points

Institutions

  • 2-2015
    • Vienna University of Technology
      • • Institute of Materials Chemistry
      • • Institute of Solid State Physics
      • • Institute of Theoretical Physics
      • • Institute of Chemical Technology, Environmental Technology and Life Sciences
      Wien, Vienna, Austria
  • 2010
    • University of Amsterdam
      • Van der Waals-Zeeman Institute
      Amsterdamo, North Holland, Netherlands
    • University of Duisburg-Essen
      Essen, North Rhine-Westphalia, Germany
    • Christian-Albrechts-Universität zu Kiel
      Kiel, Schleswig-Holstein, Germany
  • 2007
    • University of Zurich
      • Institut für Physikalische Chemie
      Zürich, Zurich, Switzerland
  • 2006
    • Technische Universität Clausthal
      • Department of Theoretical Physics
      Bergstadt-Clausthal-Zellerfeld, Lower Saxony, Germany
  • 2004
    • The University of Warwick
      • Department of Physics
      Coventry, England, United Kingdom
  • 2001
    • The Police Academy of the Czech Republic in Prague
      Praha, Praha, Czech Republic
    • Academy of Sciences of the Czech Republic
      Praha, Praha, Czech Republic
    • Medical School Hamburg
      Hamburg, Hamburg, Germany
    • University of Hamburg
      • Institute of Inorganic and Applied Chemistry
      Hamburg, Hamburg, Germany
  • 1998
    • University of Vienna
      Wien, Vienna, Austria
    • Karl-Franzens-Universität Graz
      • Institute of Physics
      Graz, Styria, Austria
  • 1997
    • Arizona State University
      Phoenix, Arizona, United States
  • 1986
    • University of Birmingham
      Birmingham, England, United Kingdom
    • University of St Andrews
      Saint Andrews, Scotland, United Kingdom