Self-Consistent Orthogonalized-Plane-Wave and Empirically Refined Orthogonalized-Plane-Wave Energy-Band Models for Cubic ZnS, ZnSe, CdS, and CdSe

First-principles orthogonalized-plane-wave energy-band calculations have been carried out for cubic ZnS, ZnSe, CdS, and CdSe, using a nonrelativistic formalism and Slater's free-electron exchange approximation. The calculations were first carried out in terms of a physically realistic trial crystal potential, and then iterated to obtain a self-consistent solution. So far as we are aware, these are the first fully convergent, fully self-consistent energy-band solutions reported for cubic II-VI semiconducting compounds. In spite of the simplified treatment of exchange effects, and the neglect of relativistic and correlation effects, the first-principles solutions are in qualitative and semi-quantitative agreement with experiment in all cases. It is shown briefly how improved solutions can be obtained by introducing small, carefully chosen empirical corrections. The adequacy of various energy-band models was tested by calculating the optical spectrum (actually ${\epsilon }_2$) and comparing this with the experimental spectrum. Actually, this comparison checks only certain features of these energy-band models. It would be helpful to have additional experimental information so that other features, such as the energy separation between principal and subsidiary conduction-band minima, could also be checked.