Multi Reference versus Coupled Cluster ab Initio Calculations for the N2 + N2 Reaction Channels

Abstract

By making use of a Grid enabled ab initio molecular simulator we have tackled the a priori study of the N2( ${}^1{\Sigma}_g^+$ ) + N2( ${}^1{\Sigma}_g^+$ ) process. A detailed analysis of the results obtained from high level ab initio (Coupled Cluster) calculation of the electronic structure of N4 for a large number of nuclear geometries has singled out the fact that Coupled Cluster calculations are insufficiently accurate when the internuclear distances of the approaching N2 diatoms are stretched, because in such cases the wavefunction of the N4 system cannot be properly described by a single determinant. For this reason we have carried out Multi Reference calculations (using the same basis set) for a large number of the nuclear geometries considered for the Coupled Cluster study. Then, a 4-atoms global potential energy surface has been worked out for use in dynamics calculations.