THE P-D HYBRIDIZATION IN THE ELECTRONIC-STRUCTURE OF ALPHA-AG2TE

The electronic structure of cr-Ag,Te is discussed, with special attent ion paid to possible roles of the p-d hybridization, on the basis of d ensity functional calculations in the local-density approximation; alp ha-Ag2Te is a typical superionic conductor, and also exhibits interest ing electronic properties. Fully self-consistent calculations based on the energy variational principle are carried out for a hypothetical c rystalline compound, Ag2Te with the antifluorite structure, making use of the linearized augmented-plane-wave method. The calculated equilib rium lattice constant agrees with a measured value within an accuracy of 5%. The self-consistent determination of the relative sizes of the augmented-plane-wave spheres leads to an energy band structure similar to that of a narrow-gap semiconductor, in accordance with experiments . Also, the magnitudes predicted for the effective masses of the elect rons and holes are almost within the experimental uncertainties. Such quantitative agreement even with the static model arises from the foll owing facts: (i) the Ag d states and the Te p states are not hybridize d to such an extent as to have a significant influence on the band-str ucture characteristics near the energy gap; and (ii) the lowest conduc tion band consists mainly of Ag and Te s states with extended characte r. Thus the p-d hybridization can hardly be considered to be the mecha nism that induces the superionic conductivity in alpha-Ag2Te.