Matrix Elements in Interband Optical Transitions

We have calculated the imaginary part of the dielectric constant ε₂ for Si and Ge using interband matrix elements obtained from the full orthogonalized-plane-wave (OPW) wave function (rather than only the plane-wave portion). The results show that for the class of semiconductor represented by Si and Ge a pseudopotential description including pseudo-wave-function matrix elements is quite adequate for obtaining the one-electron transition probabilities.