Band structures of II-VI semiconductors using Gaussian basis functions with separable ab initio pseudopotentials: Application to prediction of band offsets

We describe the implementation of a separable pseudopotential into the dual space approach for ab initio density-functional calculations using Gaussian basis functions. We apply this Gaussian dual space method (GDS/DFT) to the study of II-VI semiconductors (II=Zn, Cd, Hg; VI=S, Se, Te, Po). The results compare well with experimental data and demonstrate the general transferability of the separable pseudopotential. We also introduce a band-consistent tight-binding (BC-TB) model for calculating the bulk contributions to the valence-band offsets (VBO's). This BC-TB approach yields good agreement with all-electron ab initio GDS/DFT results. Comparisons between BC-TB results of VBO obtained with and without p-d coupling demonstrate quantitatively the importance of d electrons and cation-d-anion-p coupling in II-VI systems. Agreement between ab initio results and experimental results is excellent.