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

Ab initio band structure calculations were performed for the low-temperature modifications of the silver chalcogenides beta-Ag2Se, beta-Ag2Te and the ternary compound beta-Ag3AuSe2 by the local spherical wave (LSW) method. Coordinates of the atoms of beta-Ag2Se and beta-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 beta-Ag3AuSe2 is a semiconductor, while beta-Ag2Se and beta-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. beta-Ag2Se and beta-Ag2Te have a very low DOS in the energy range from about -0.1 to +0.5 eV. The calculated effective mass beta-Ag2Se is about 0.1-0.3 m(e) for electrons and 0.75 m(e) for holes, respectively. (C) 2002 Elsevier Science Ltd. All rights reserved.