The parametrized second-order Green function times screened interaction (pGW2) approximation for calculation of outer valence ionization potentials

In this paper we introduce a parameter to the second-order Green function times screened-interaction of Hedin's (GW2). The valence ionization potentials (IPs) predicted by the parametrized GW2 (pGW2) scheme compare well with experiment for a collection of 45 valence IPs for 13 small molecules. With the cc-pVTZ basis set the average absolute deviation between theoretical prediction and experiment is 0.25 eV. With the smaller cc-pVDZ basis set using the option scaling parameter (0.48) obtained from the cc-pVTZ basis set, the average absolute deviation is 0.32 eV. We have also calculated the 10 valence IPs of glycine at the geometries of its two lowest energy conformers. Our results confirm that comformer I is the global minimum, The predicted valence IPs of glycine I agree excellently with experiment (average absolute deviation 0.20 eV), and lead to are assignment of the photoelectron spectrum. (C) 1997 Elsevier Science B.V.