Quasiparticle Excitation Spectrum for Nearly Free Electron Metals.

The quasiparticle excitation spectrum is calculated for the nearly free electron metals Li, Na, and Al by evaluation of the electron self energy operator within the GW approximation and a generalized plasmon pole model. The calculated quasiparticle energies for Na and Al are in excellent agreement with angle resolved photoemission experiments. For Na in particular, the occupied bandwidth is significantly narrower than the free electron value, as found in experiment. Inclusion of exchange and correlation effects in the dielectric matrix is show to decrease the bandwidth relative to the RPA result by a significant amount. Local field effects, reflected in the off diagonal elements of the dielectric matrix, are found to have little effect on the band structure of these simple metals.