The Experts below are selected from a list of 3897 Experts worldwide ranked by ideXlab platform

Yves Joly - One of the best experts on this subject based on the ideXlab platform.

  • X-ray absorption near-edge structure calculations beyond the Muffin-Tin Approximation
    Physical Review B, 2001
    Co-Authors: Yves Joly
    Abstract:

    A new scheme for calculating the x-ray absorption near edge structure (XANES) based on the finite-difference method is proposed. It allows completely free potential shape and, in particular, is not constrained to the Muffin-Tin Approximation. In our approach, the calculation of the final states is performed in real space. The Schr\"odinger equation is solved in a discrete form on the node points of a three-dimensional grid. The unknowns are the values of the wave functions at the grid points. The validity of the method is shown on two different systems the metallic copper and the carbon monoxide molecule; then, the differences resulting from Muffin-Tin and non-Muffin-Tin calculations are shown on different typical molecules.

  • X-Ray Absorption Near Edge Structure Calculation Beyond the Muffin-Tin Approximation
    Journal De Physique Iv, 1997
    Co-Authors: Yves Joly
    Abstract:

    A new scheme of calculation for X-ray Absorption Near Edge Structure (XANES) based on the finite-difference method is proposed. It permits a potential shape completely free and in particular not constrained in the Muffin-Tin Approximation. In our approach, the calculation of the final states is performed in real space. The spherical areas around the atomic nuclei are reduced to very small spheres where the Approximation is in any case valid. Between the spheres, the Schrodinger equation is solved in a discrete form on the node points of a three-dimensional grid. The unknowns are the values of the wave function at the grid points. Results on oxides show good agreement between experiment and theory. This procedure can give access to new parameters such as the charge exchange between atoms.

  • Finite-difference method for the calculation of low-energy-electron diffraction.
    Physical review letters, 1992
    Co-Authors: Yves Joly
    Abstract:

    A new scheme of calculation avoiding the Muffin-Tin Approximation is presented for low-energy-electron diffraction. The finite-difference method is then used to solve the Schrodinger equation. A simple superposition potential and a nonuniform three-dimensional grid of points yields satisfactory experiment-theory agreement for the Cr(100)-(1×1)N surface, with geometrical parameter values close to the ones found in a standard study. An optimization of the charge exchange gives a 1.3 electron transfer from chromium to nitrogen

Z. Liu - One of the best experts on this subject based on the ideXlab platform.

  • New formalism for the SCF-Xα-SW model with application to large molecular systems or atomic clusters
    Chemical Physics Letters, 1993
    Co-Authors: Wei Ren, Z. Liu
    Abstract:

    Abstract A new formalism for the SCF-Xα-SW model suitable for treatment of some large molecular systems or atomic clusters is presented via the efficient recursive aggregate T -matrix algorithms developed recently in electromagnetics. The space is divided into two regions and the original problem is treated as a two-body scattering problem: one scatterer is an assembly of the N atoms characterized by the aggregate T -matrix, the other is the outer sphere in the muffin tin Approximation. This method reduces the order of the secular matrix and the computational complexity of the homogeneous linear system of equations.

Wei Ren - One of the best experts on this subject based on the ideXlab platform.

  • New formalism for the SCF-Xα-SW model with application to large molecular systems or atomic clusters
    Chemical Physics Letters, 1993
    Co-Authors: Wei Ren, Z. Liu
    Abstract:

    Abstract A new formalism for the SCF-Xα-SW model suitable for treatment of some large molecular systems or atomic clusters is presented via the efficient recursive aggregate T -matrix algorithms developed recently in electromagnetics. The space is divided into two regions and the original problem is treated as a two-body scattering problem: one scatterer is an assembly of the N atoms characterized by the aggregate T -matrix, the other is the outer sphere in the muffin tin Approximation. This method reduces the order of the secular matrix and the computational complexity of the homogeneous linear system of equations.

Dimitrios A. Papaconstantopoulos - One of the best experts on this subject based on the ideXlab platform.

  • First-principles study of superconductivity in high-pressure boron
    Physical Review B, 2002
    Co-Authors: Dimitrios A. Papaconstantopoulos, Michael J. Mehl
    Abstract:

    We study superconductivity in boron using first-principles LAPW calculations, the rigid-Muffin-Tin Approximation, and the McMillan theory. Our results point to an electron-phonon mechanism producing transition temperatures near 10 K at high pressures, in agreement with recent measurements.

  • Electronic structure of the BaA1-xBxO3 (A, B = Pb, Bi, Sn, Sb) alloy systems: Implications for superconductivity
    Physica C-superconductivity and Its Applications, 1994
    Co-Authors: J.p. Julien, David J. Singh, Dimitrios A. Papaconstantopoulos, Warren E. Pickett, Françoise Cyrot-lackmann
    Abstract:

    Abstract Coherent potential Approximation studies of the electronic structure of the BaA1-xBxO3 (where A and B are different combinations of the elements Pb, Bi, Sn and Sb) alloy systems have been performed with accurate tight-binding hamiltonians. The calculations show how semiconducting BaSnO3 evolves into a metal upon alloying with Sb or Bi. Common characteristics of the densities of states are pointed out. Using the rigid Muffin-Tin Approximation an analysis of the superconducting properties is given.

  • Electronic structure of Ba(Sn,Sb)O3: Absence of superconductivity.
    Physical review. B Condensed matter, 1991
    Co-Authors: David J. Singh, Dimitrios A. Papaconstantopoulos, J.p. Julien, Françoise Cyrot-lackmann
    Abstract:

    The electronic structures of ${\mathrm{BaSnO}}_{3}$, ${\mathrm{BaSbO}}_{3}$, and ${\mathrm{BaPbO}}_{3}$, calculated using an extended general-potential linearized augmented-plane-wave method, are reported. The electronic structures of ${\mathrm{BaSnO}}_{3}$ and its 6s analog ${\mathrm{BaPbO}}_{3}$ are found to be very different, explaining the absence of superconductivity in the Ba(Sn,Sb)${\mathrm{O}}_{3}$ system. These differences are explained by a combination of the relativistic lowering of the 6s states and ion-size effects. Muffin-Tin-Approximation augmented-plane-wave calculations for ${\mathrm{BaSnO}}_{3}$ are also reported and the utility of the Muffin-Tin Approximation for this and similar materials is discussed in terms of the differences between the two sets of calculations.

Yu. V. Ilyasov - One of the best experts on this subject based on the ideXlab platform.

  • Electronic structure of the diamondlike systems BN_1−x Me_x (Me = Ti, Cr, Mn, Fe, Ni, Cu)
    Physics of the Solid State, 1997
    Co-Authors: V. V. Ilyasov, I. Ya. Nikiforov, Yu. V. Ilyasov
    Abstract:

    The local coherent potential method is used within the framework of multiple scattering theory to calculate the electron energy structure of the diamondlike systems BN_1− x Me_x (Me is a 3 d transition metal) with the ZnS structure. We used the cluster version of the muffin tin Approximation to calculate the crystal potential. The framework of a single Approximation is used to compare the electronic energy structure of ternary and binary boron-nitride systems. The width of the hybridized band of the ternary systems BN-Me (Me = Cr, Mn, Fe, Cu) is greater than in the binary system by more than 8 eV and is due to the resultant B-Me interaction.

  • Electronic structure of the diamondlike systems BN1−xMex (Me = Ti, Cr, Mn, Fe, Ni, Cu)
    Physics of the Solid State, 1997
    Co-Authors: Victor V. Ilyasov, I. Ya. Nikiforov, Yu. V. Ilyasov
    Abstract:

    The local coherent potential method is used within the framework of multiple scattering theory to calculate the electron energy structure of the diamondlike systems BN1−xMex (Me is a 3d transition metal) with the ZnS structure. We used the cluster version of the muffin tin Approximation to calculate the crystal potential. The framework of a single Approximation is used to compare the electronic energy structure of ternary and binary boron-nitride systems. The width of the hybridized band of the ternary systems BN-Me (Me = Cr, Mn, Fe, Cu) is greater than in the binary system by more than 8 eV and is due to the resultant B-Me interaction.