Optimization of both resonance structures of the glyoxal radical cation by means of the Valence Bond Self-Consistent Field method

Abstract

The Valence Bond Self-Consistent Field (VBSCF) method is used to form various wave functions of distinct quality, in which the resonance structures of the glyoxal radical cation are explicitly present. These wave functions are fully optimized, and the corresponding total energies are calculated for several nuclear geometries of the ion. It is shown that the potential energy surfaces of the VBSCF functions are continuous on symmetry lowering, whereas RHF and CASSCF surfaces expose gaps. Localization of the unpaired electron either on both oxygen atoms, in case ofC 2h symmetry, or on a single oxygen atom, in case ofC s symmetry, is well described by the VBSCF functions, and a smooth transition between the two states is obtained.