Multiconfigurational electron propagator (MCEP) ionization potentials for general open shell systems

Abstract

We have developed a multiconfigurational electron propagator (MCEP) technique for the theoretical determination of ionization potentials for general open shell and highly correlated atomic and molecular systems. In order to do this, we have used and extended the generalized spin-symmetry adapted operators of Pickup and Mukhopadhyay. To properly account for correlation effects we have additionally included ionization and electron affinity operators analogous to the ‖Γ〉〈0‖ state transfer operators necessary in multiconfigurational linear response. MCEP ionization potentials and ionization process probabilities have been evaluated for both O2 and N2 and used to carry out detailed examination and interpretation of the respective PES and ESCA spectra. The MCEP results are extremely encouraging for both principal and shake-up I.P.′s. For example, using 〈5s4p1d〉 contracted Gaussian basis sets the principal valence ionization potentials to bound ionic states are calculated within ±0.3 eV of experiment for both N2 and O2. For several I.P.′s the breakdown of the single particle picture is calculationally demonstrated, e.g., the intensity of the 2σu electron removal process to give 2Σ−u states in O2 is almost equally divided between two ESCA peaks. One of these peaks is the previously unassigned A peak in the ESCA spectrum.