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Theoretical results on the structural and the electronic properties of MgS and MgSe are presented. The calculations were made using the full-potential linear muffin-tin orbitals (FP-LMTO) method augmented by a plane wave (PLW) basis. It was found that the electronic properties in the B1, B3 and B4 structures of these magnesium chalcogenides show good agreement compared to other works. Through these results the power of these calculation methods applied to the magnesium chalcogenides was confirmed.

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The electronic and optical properties of M(2)S (M = Li, Na, K and Rb) compounds in the cubic antifluorite structure have been calculated, using a full relativistic version of the full-potential augmented plane-wave plus local orbitals method based on density functional theory, within both the local density approximation (LDA) and the generalized gradient approximation (GGA). Moreover, the Engel-Vosko GGA formalism (EV-GGA) is applied so as to optimize the corresponding potential for band structure calculations. The calculated equilibrium lattices and bulk moduli are in good agreement with the available data. Band structure, density of states, electron charge density and pressure coefficients of energy gaps are given. Results obtained for band structure using EV-GGA are larger than those with LDA and GGA. It is found that the spin-orbit coupling lifts the triple degeneracy at the Γ point and the double degeneracy at the X point. The analysis of the electron charge density shows that the M-S bonds have a significant ionic character. The complex dielectric functions ε(2)(ω) for alkali metal sulfides were calculated for radiation up to 30 eV and the assignment of the critical points to the band structure energy differences at various points of the Brillouin zone was made. The pressure and volume dependence of the static dielectric constant and the refractive index are calculated.

The structural phase transformations of CdS and CdSe under high pressure are studied by using the local approximation to the density functional theory, and the one-electron equations are solved by means of the full-potential linear muffin-tin-orbital method FP-LMTO. CdS and CdSe are found to have nearly similar structural systematics under high pressure. In CdS, the Pmmn phase is predicted after the rocksalt structure, and in CdSe the Cmcm structure is thermodynamically stable after the rocksalt structure. We also find a thermodynamic stability range for the CsCl phase of CdSe. The structural properties of the zincblende, wurtzite, rocksalt, Pmmn, and Cmcm phases are presented.

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