Low-lying quintet states of the cobalt dimer

Abstract

Low-lying quintet states of Co2 have been studied using CCSD, CCSD(T), MCSCF, and the Generalized Van Vleck Perturbation Theory (GVVPT2) variant of second-order multireference perturbation theory. Equilibrium bond lengths and harmonic vibrational frequencies of the lowest 5Δ g and states have been calculated and compared with the results of previous studies. A balanced treatment of nondynamic and dynamic correlation effects has been shown to be of crucial importance for the correct description of the considered states. Based on the GVVPT2 calculations, the l5Δ g state is predicted to lie lower than by about 0.3 eV.