QUANTUM-MECHANICAL HARTREE-FOCK STUDY OF THE ELASTIC PROPERTIES OF LI2S AND NA2S

The binding energy and elastic constants of Li2S and Na2S are investig ated at an ab initio all electron Hartree-Fock level. The comparison b etween calculated and experimental values leads to satisfactory agreem ent for Li2S and a substantial difference in the Na2S case. The compar ative evolution of the elastic constants in the series of alkaline oxi des and sulphides with the size of the cation seems to indicate that t he discrepancy is mainly due to an overestimation of the experimental elastic constants of Na2S.