Improved calculations of ionization potentials of closed-shell molecules

Abstract

A theory recently developed for atoms and molecules is applied to the calculation of the main poles of one-particle Green's functions in the low-energy region and their pole strengths for the molecules F₂, H₂O, C₂H₂ and H₂CO. The poles corresponding to occupied orbitals compare well with the experimental vertical ionization potentials (VIP's). In particular the sequence of the VIP's of F₂ which is not reproduced by Koopmans' theorem (breakdown) is re-established. The corresponding pole strengths are found to have values around 0·9.