Perturbation corrections to Koopmans' theorem. I. Double-zeta Slater-type-orbital basis

Abstract

Ordinary third‐order Rayleigh‐Schrödinger perturbation theory is used to evaluate vertical ionization potentials of closed‐shell molecules. The method is tested with double‐zeta calculations on H₂O, CH₂, NH₃, H₂CO, and F₂O. The results are compared with the ΔSCF method and discussed. On the basis of our calculations, we confirm the suggested alternative assignment for the photoelectron spectrum of F₂O, instead of the original assignment based on Koopmans' theorem.