Optical response of uniaxial semiconductors. I. Theory and calculational methods

A rigorous derivation of the one-electron ε₂ tensor for noncubic semiconductors is given, starting from the general many-electron problem. The results derived from Frenkel's variational principle and the one-electron Green's-function theory indicate that the same self-energy operator must be used both in the equation of motion and in calculating the bands. The calculational methods used for the optical-response spectra of uniaxial semiconductors are described. The sum rules are found to be accurately valid for ε₂, absorption coefficient, and -Imε^-1 of ZrS₂, ZrSe₂, and Te.