Electronic excitations in semiconductors: Variational Green's-function approach

Abstract

We develop a Green's-function method for calculating electronic excitations in semiconductors. It is variational in character and takes full account of the local part of the correlation hole as well as the long-ranged polarization cloud. Both contribute significantly to the quasiparticles and their energies. The method is based on the Sauermann functional, the stationary point of which is the one-particle Green's function. For the case of a simple model, a connection is established to an earlier method which required the computation of correlated wave functions in order to obtain the excitation energies. Furthermore, we relate the present approach to the single-mode approximation of Overhauser and others which was devised for describing electron correlations in nearly homogeneous systems.