Multireference State-Specific Coupled-Cluster Theory and Multiconfigurationality Index. BH Dissociation

Abstract

Multiconfigurationality index calculated for the coupled-cluster wave function based on an algorithm developed using a computer-aided generation approach is applied to analyze the multireference state-specific coupled-cluster method with the CAS reference (i.e. the so called the CAS(n,m)CCSD approach). The numerical results concern dissociation of the BH molecule where at larger displacement from the equilibrium significant quasi-degeneracy arises. The analysis shows that the CAS(n,m)CCSD approach performs very well in such a situation.