Elastic constants and electronic structure of alkaline-earth chalcogenides. Performances of various hamiltonians

The elastic constants and electronic structure of alkaline-earth chalcogenides MX (M≡Mg, Ca, Sr and X≡O, S, Se) are investigated at the quantum mechanical level with the periodic Crystal 98 program. All-electron and (or) pseudopotential Gaussian-type basis sets are used for light (Mg, Ca, O, S) and (or) heavy (Ca, Sr, Se) atoms, respectively. The calculations are performed at the Hartree–Fock (HF), density functional (DF) and hybrid (B3LYP) levels of theory. As regards DF, the local density (LDA) and generalized gradient (GGA) approximations are used. The performances of the various hamiltonians are discussed with respect to the experimental data which are only available for the alkaline-earth oxides. Very good agreement with experiment has been found for the gradient-corrected DF and B3LYP schemes. The extension to the sulfide and selenide families permits to discuss the ionicity and lattice constant effects.