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Sökning: swepub > Johansson Börje > Refereegranskat > Kollar J.

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31.
  • Punkkinen, M. P. J., et al. (författare)
  • Magnetism of (FeCo)Si alloys : Extreme sensitivity on crystal structure
  • 2006
  • Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 73:2
  • Tidskriftsartikel (refereegranskat)abstract
    • Theoretical results for (FeCo)Si substitutional random alloys, obtained within the framework of the exact muffin-tin orbitals method in combination with the coherent potential approximation, are presented. For concentration range 0.1 < x < 0.9, the magnetic structure of Fe1-xCoxSi is found to be almost degenerate, which is reflected in extreme sensitivity of the local magnetic moments on the internal structure parameters and lattice constant. Results are analyzed and discussed using Stoner, covalent magnetism, and rigid band models. In Fe-rich and in Co-rich alloys, the composition dependence of the magnetic moments can be understood in terms of a simple model. It is shown that disorder has a significant effect on magnetism in (FeCo)Si alloys.
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32.
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33.
  • Ropo, M., et al. (författare)
  • The chemical potential in surface segregation calculations : AgPd alloys
  • 2006
  • Ingår i: Surface Science. - : Elsevier BV. - 0039-6028 .- 1879-2758. ; 600:4, s. 904-913
  • Tidskriftsartikel (refereegranskat)abstract
    • We put forward a technique for calculating the surface segregation profile in substitutional disordered alloys. The surface internal energy and the effective bulk and surface chemical potentials are calculated using the full charge density exact muffin-tin orbitals method, combined with the coherent potential approximation. The application of our approach is demonstrated to the close-packed surface of AgcPd1-c random alloys with 0 < c < 1. The surface concentration profile, surface energy and segregation energy are investigated as functions of bulk composition. The present results are compared with former theoretical and experimental data. It is found that at low temperature, Ag segregates to the surface layer for the entire bulk composition range. At 0 K, the subsurface layer contains 100% Pd for c <= 0.4, and somewhat more than (2c - 1) Ag in alloys with c > 0.5. The temperature dependence of the segregation profile is significant for I'd rich alloys and for alloys with intermediate concentrations. At temperatures >= 600 K, the subsurface layer is obtained to be almost bulk like.
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34.
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35.
  • Vitos, Levente, et al. (författare)
  • Application of the exact muffin-tin orbitals theory : the spherical cell approximation
  • 2000
  • Ingår i: Computational materials science. - 0927-0256 .- 1879-0801. ; 18:1, s. 24-38
  • Tidskriftsartikel (refereegranskat)abstract
    • We present a self-consistent electronic structure calculation method based on the exact muffin-tin orbitals (EMTO) theory developed by O.K. Andersen, O. Jepsen and G. Krier [in: V. Kumar, O.K. Andersen, A. Mookerjee (Eds.), Lectures on Methods of Electronic Structure Calculations, Word Scientific, Singapore, 1994, pp. 63-124] and O.K. Andersen, C. Arcangeli, R.W. Tank, T. Saha-Dasgupta, G. Krier, O. Jepsen and I. Dasgupta [Mater. Res. Sec. Symp. Proc. 491 (1998) 3-34]. The EMTO theory can be considered as an improved screened KKR (Korringa-Kohn-Rostoker) method which is able to treat large overlapping potential spheres. Within the present implementation of the EMTO theory the one-electron equations are solved exactly using Green's function formalism, and Poisson's equation is solved within the spherical cell approximation (SCA). To demonstrate the accuracy of the SCA-EMTO method, test calculations have been carried out.
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36.
  • Vitos, Levente, et al. (författare)
  • Application of the exact muffin-tin orbitals theory: the spherical cell approximation
  • 2000
  • Ingår i: COMPUTATIONAL MATERIALS SCIENCE. - : ELSEVIER SCIENCE BV. - 0927-0256. ; 18:1, s. 24-38 Language: English
  • Tidskriftsartikel (refereegranskat)abstract
    • We present a self-consistent electronic structure calculation method based on the exact muffin-tin orbitals (EMTO) theory developed by O.K. Andersen, O. Jepsen and G. Krier [in: V. Kumar, O.K. Andersen, A. Mookerjee (Eds.), Lectures on Methods of Electron
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37.
  • Vitos, Levente, et al. (författare)
  • Exchange energy in the local Airy gas approximation
  • 2000
  • Ingår i: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 62:15, s. 10046-10050
  • Tidskriftsartikel (refereegranskat)abstract
    • The Airy gas model of the edge electron gas is used to construct an exchange-energy functional that is an alternative to those obtained in the local-density and generalized-gradient approximations. Test calculations for rare-gas atoms, molecules, solids, and surfaces show that the Airy gas functional performs better than the local-density approximation in all cases and better than the generalized-gradient approximation for solids and surfaces.
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38.
  • Vitos, Levente, et al. (författare)
  • Exchange energy in the local Airy gas approximation
  • 2000
  • Ingår i: PHYSICAL REVIEW B. - : AMERICAN PHYSICAL SOC. - 0163-1829. ; 62:15, s. 10046-10050 Language: English
  • Tidskriftsartikel (refereegranskat)abstract
    • The Airy gas model of the edge electron gas is used to construct an exchange-energy functional that is an alternative to those obtained in the local-density and generalized-gradient approximations. Test calculations for rare-gas atoms, molecules, solids,
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39.
  • Vitos, L., et al. (författare)
  • Local kinetic-energy density of the Airy gas
  • 2000
  • Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 61:5, s. art. no.-52511
  • Tidskriftsartikel (refereegranskat)
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40.
  • Vitos, Levente, et al. (författare)
  • Local kinetic-energy density of the Airy gas - art. no. 052511
  • 2000
  • Ingår i: PHYSICAL REVIEW A. - : AMERICAN PHYSICAL SOC. - 1050-2947. ; 6105:5, s. 2511-+ Language: English
  • Tidskriftsartikel (refereegranskat)abstract
    • The Airy gas model is used to derive an expression for the local kinetic energy in the linear potential approximation. The expression contains an explicit Laplacian term 2/5((h) over bar(2)/2m)del(mu)(2)(r) that, according to jellium surface calculations,
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  • Resultat 31-40 av 46

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