Density-Functional Theory of Excitation Spectra of Semiconductors: Application to Si

This Letter presents a general approach to calculation of the quasiparticle excitation energies of semiconductors which includes the energy dependence of the self-energy with a local density-functional approach. Both direct and indirect band gaps in Si are in much better agreement with experiment than are the bands from the ground-state theory. The relatively large corrections arise only after the dielectric screening of the electron gas is modified to account for a gap in the excitation spectrum.