FIRST-PRINCIPLES STUDY OF STRUCTURAL AND ELECTRONIC PROPERTIES OF ALKALI METAL CHALCOGENIDES: M2CH[M: LI, NA, K, RB; CH: O, S, SE, TE]

Abstract

Ground-state structural properties of alkali metal selenides and tellurides (M2X) [M: Li, Na, K, Rb; X: Se, Te] have been studied in the framework of density functional theory for the first time using local density approximation, Perdew–Burke–Ernzerhof generalized gradient approximation (GGA) and Wu–Cohen (WC) GGA parameterization schemes. Also structural properties of alkali metal oxides and sulfides (M2X) [M: Li, Na, K, Rb; X: O, S] have been reinvestigated using WC GGA. Electronic band structures of alkali metal chalcogenide compounds have been calculated using the aforementioned schemes as well as the modified GGA proposed by Engel and Vosko. The calculated structural parameters for all 16 materials have been compared with earlier theoretical and experimental results, and certain trends are discussed. Furthermore, electronic density of states for these compounds has also been presented herein and behavior in electronic properties analyzed. Li, K and Rb chalcogenides have been found to have indirect bandgap, whereas Na chalcogenides appear to have direct bandgap.