Quasiparticle energies in small metal clusters

We have calculated the quasiparticle energies of sodium and potassium clusters using the jellium-sphere-background model for positive-ion cores and the Hedin GW approximation for the self-energies of valence electrons. In the calculation of the screened Coulomb interaction, a new general method to approximate the excitation spectrum of the interacting many-body systems is introduced. The calculated ionization potentials and quasiparticle energies are significantly improved compared to calculations based on the Hohenberg-Kohn-Sham local-density-functional theory.