Development of a computational scheme for electronic structure of compounds taking account of lattice-induced anisotropic effects and difference in the atomic species

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We have developed a variational augmented plane wave (APW) method for the electronic states in solids. It copes with such probelms as the conventional APW method encounters when applied to materials with open structure (e.g., Si) and/or with highiy asymmetric species of atoms (e.g.Li_2Te). The new scheme based on the energy variational principle in the density-functional theory determines the Kohn-Sham potentials in the framework of the muffin-tin (MT) spproximation through minimization of the total energy of a system. Thus the asymmetric problem in choosing the MT radii is variationally solved and the lattice-induced anisotropic effects are taken into account by exactly calculating the Coulombic energy. It was demonstrated that the variational treatment of the MT radii significantly improves agreement with experimental results for the lattice constant, the cohesive energy and the band structure in the alkaline tellurides, especially in Li_2Te, the most asymmetric compound among them. … More We also applied the variaional APW method to the electronic strutture of Ag_2Te and Cu_2Te to have an inight into the microscopic origin of the superionic conductivity ; Ag_2Te in the alpha phase is a typical superionic conductor. The present calculation accurately reproduces the electronic properties of the alpha-Ag_2Te with characteristics of a narrow gap semiconductor. We directed our special attention to the difference in the closed-shell structures between thenoble-metal ions (d-shell) and the alkali ions (sp-shell) embedded in the Te sublattice with a p-band. Comparison of the results for Ag_2Te and Cu_2Te enabled us to discuss possible effects of the p-d hybridization on the onset of the superionic conductivity. We thus inferred that combination of polarizability of the d shell and weakness of the p-d hybridization plays a primary role in giving rise to the superionic conductivity. The activation energies for the ionic diffusion were estimated in good agreement with the experiments. Less