Electronic and elastic properties of alkali-metal sulphides-Li2S and Na2S

From first-principles, the electronic and elastic properties of alkali-metal sulphides (Li2S, Na2S), with emphasis on the plane-wave pseudopotential method and the inclusion of the non-linear core correction for exchange and correlation have been investigated. At ambient condition, these compounds are found to crystallize in cubic anti-fluorite structure. This method is found to describe the properties of these materials rather well. In most of the cases, obtained ground state properties are in good agreement with experimental and theoretical results. From the electronic structure calculations, we found that Li2S is indirect band gap semiconductor whereas Na2S is direct band gap semiconductor within local density approximation (LDA).