One-body Green's function for atoms and molecules: theory and application

The one-body Green's function is investigated by expanding the self-energy part up to third order. On this level some properties of the diagrams of the self-energy part are discussed. To estimate the contribution of higher orders of the self-energy part an effective time dependent interaction is introduced. It is found that the main contributions due to this interaction can be determined by considering the analytic properties of second and third order terms only. The numerical effort required can thus be strongly reduced. The theory is applied to calculate the vertical ionization potentials of B2H6. The calculation of the pole strengths shows that one may expect satellite lines in the photoelectron spectrum of B2H6 with about 10% of the intensity of the principal valence lines due to excitations accompanying ionization.