Improved calculations of ionization potentials of closed-shell molecules

Abstract

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.