Investigations of nonlocal exchange and correlation effects in metals via the density-functional formalism

The density-functional formalism of Hohenberg, Kohn, and Sham is used to investigate the effects of nonlocal exchange and correlation on the Fermi surface of a simple-cubic metal. The "nonlocal" Fermi surface is obtained by solving the Dyson equation for the quasiparticle states on the Fermi surface with the nonlocal self-energy approximated according to the density-functional scheme in the presence of an external model pseudopotential. This was done by using the corresponding local theory to define a zeroth-order Hamiltonian which provides basis functions to solve the nonlocal eigenvalue problem. It was found that the maximum Fermi-surface distortions obtained from the nonlocal theory were substantially reduced from the local theory, as experiments suggest. The calculations were carried out in the random-phase approximation.