Occupied quasiparticle bandwidth of potassium

The quasiparticle energies and occupied bandwidth of potassium are calculated with a first-principles self-energy approach. The valence-electron self-energy operator is obtained in the GW approximation, evaluating the self-energy to first order in the screened Coulomb interaction W and the single-particle Green function G. Vertex corrections are not included in this approach. We treat the electron-ion interaction with the ab initio pseudopotential scheme. The static dielectric screening matrix which includes the effects of exchange and correlation is obtained as a ground-state quantity from a local-density (LDA) calculation, and is extended to finite frequencies by a generalized plasmon-pole model. The electron Green function is obtained in the quasiparticle approximation by use of the self-consistent quasiparticle energies. We find that the calculated occupied bandwidth is reduced from a LDA Kohn-Sham value of 2.27 eV to 1.58±0.1 eV. This result is consistent with existing soft-x-ray emission data. It is also in agreement with a recent photoemission experiment.