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 properties 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. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)