First-principles electronic structure of Si, Ge, GaP, GaAs, ZnS, and ZnSe. II. Optical properties

The interband optical properties of Si, Ge, GaP, GaAs, ZnS, and ZnSe were calculated using ab initio self-consistent energy bands and wave functions obtained from the previous paper (paper I). Qualitatively good agreement with experiment is found, but all peak positions are shifted to lower energies since the local-density approximation underestimates the optical band gaps. Agreement with experiment with regard to line shape and peak position can be improved using an empirical energy-dependent self-energy correction as appears in the Sham-Kohn local-density theory of excitation. After examining the possible effects of lifetime broadening, our results indicate that additional many-body, excitonic, and local-field corrections must be included to achieve quantitative agreement in the intensity of certain features in the optical spectra.