Crystal Potential and Energy Bands of Semiconductors. IV. Exchange and Correlation

Abstract
The contribution of exchange and correlation to one-electron self-energies in a periodic potential is treated using the generalized Koopmans' theorem. Numerical estimates are made for effects due to covalent bonds in Si. In the random phase approximation, matrix elements of the valence exchange and correlation operators are found to be weakly momentum dependent and spatially similar to the valence Coulomb potential. Near the energy gap the combined exchange and correlation "potential" in Si is remarkably similar to the Slater free-electron exchange potential.