Semiempirical calculations of molecular valence-shell ionization potentials by linear response theory based on coupled clusters

Abstract

The recently proposed linear response theory based on coupled clusters (CCLRT) has been applied within the framework of different semiempirical approximations for the calculation of both inner and outer valence ionization potentials of a number of molecules. CCLRT with CNDO/S parametrization leads to the best results. The breakdown of Koopmans' theorem is generally observed in the inner valence region. The shake-up structure arising due to configuration mixing remains more or less unchanged in different parametrizations. The approximate ionization strength and also the important shakeup configurations have been reported.