First-principles study of electronic structure and ground-state properties of alkali-metal sulfides -: Li2S, Na2S, K2S and Rb2S

First-principles calculations have been performed to investigate the electronic structure and ground-state proper-ties of alkali-metal sulfides Li2S, Na2S, K2S and Rb2S using the tight-binding linear muffin-tin orbital (TB-LMTO) method. At ambient conditions these compounds are found to crystallize in the cubic antifluorite (anti-CaF2-type) structure. The exchange correlation energy is described in the local density approximation (LDA) using the von-Barth and Hedin parameterization scheme. The calculated ground-state properties of these compounds such as equilibrium lattice parameter and bulk modulus are in agreement with the other theoretical calculations and experiment results. From the results of the electronic-structure calculations, we find that Li2S, K2S and Rb2S are indirect bandgap semiconductors, whereas Na2S is found to be a direct bandgap semiconductor. (C) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.