Quasiparticle energies in small alkali-metal clusters

The authors have calculated the quasiparticle energies of sodium and potassium clusters using the jellium-sphere-background model for the positive ion cores. The electron self-energy is evaluated in first order in the screened Coulomb interaction with local field effects included. Results show significant improvements over the Kohn-Sham eigenvalues in the local-density-functional theory both for the occupied and for the unoccupied quasiparticle states. The theory is found to give the correct size dependencies for quasiparticle energies in the finite systems.