Ab initio band structure calculations of the low-temperature phases of Ag2Se, Ag2Te and Ag3AuSe2 Original Research Article

Ab initio band structure calculations were performed for the low-temperature modifications of the silver chalcogenides β-Ag2Se, β-Ag2Te and the ternary compound β-Ag3AuSe2 by the local spherical wave (LSW) method. Coordinates of the atoms of β-Ag2Se and β-Ag3AuSe2 were obtained from refinements using X-ray powder data. The structures are characterized by three, four and five coordinations of silver by the chalcogen, a linear coordination of gold by Se, and by metal–metal distances only slightly larger than in the metals. The band structure calculations show that β-Ag3AuSe2 is a semiconductor, while β-Ag2Se and β-Ag2Te are semimetals with an overlap of about 0.1–0.2 eV. The Ag 4d and Au 5d states are strongly hybridized with the chalcogen p states all over the valence bands. β-Ag2Se and β-Ag2Te have a very low DOS in the energy range from about −0.1 to +0.5 eV. The calculated effective mass β-Ag2Se is about 0.1–0.3 me for electrons and 0.75 me for holes, respectively.