Quasiparticle energies in clusters determined via total-energy differences: Application to C-60 and Na-4

Quasiparticle energies of fullerene C-60 and sodium tetramer Na-4 molecules have been successfully determined through cluster total-energy differences, performed within a density-functional theory of neutral and charged systems. Self-energy corrections to the density-functional theory-local-density approximation highest occupied molecular orbital-lowest unoccupied molecular orbital gap of the order of 3 eV in both clusters result in good agreement with the experiments for the fullerene molecule, while for the sodium tetramer the comparison with previous theoretical results and the experiment is something less satisfactory. The computational effort required by the present method results in orders of magnitude smaller than those associated with different Hamiltonians, thus allowing one to easily calculate quasiparticle spectra of large systems.