Self-consistent ab initio studies of the electronic-energy-band structure of cubic CdS are reported within the local-density-functional (LDF) formalism. All electrons are included using our previously reported linear-combination-of- atomic-orbitals method in a numerical basis representation. In the first set of calculations we employ the same lattice constant, exchange (only) potential, and computational parameters as were used by Stukel et al. in their early self-consistent orthogonalized-plane-wave (SCOPW) investigation so that a direct comparison of results can be made and the validity of the SCOPW approach for covalently bonded 4 d systems can be assessed. In the second set of calculations, the Stukel et al. computational restrictions are relaxed, a more accurate lattice parameter is employed, and the Kohn-Sham exchange and the Singwi et al. correlation potential are used to obtain the local-density formalism solutions to the band problem, including variation of the band structure and related properties with pressure (change of lattice constant). Comparison with optical and x-ray and uv photoemission experiments for excitations of both the s - p and metal d bands in the 5-19 eV region indicate very good agreement. The direct gap at is, however, found to be 0.5 eV (25%) too small, a discrepancy similar to that previously found in nonempirical studies for other heteropolar insulators (e.g., Ne and LiF). This is traced to the neglect of the different orbital relaxation at the 25 and 1 band edges and to the noncancellation of the self-interaction terms characteristic of the local-density potential. Simple atomic total-energy models for these effects are shown to bring this gap into good agreement with experiment. It is concluded that a first-principles (parameter-free) exchange and correlation LDF model describes very well the main electronic-structure features of the system.
ASJC Scopus subject areas
- Condensed Matter Physics