Full effect of triples in a valence universal multi-reference coupled cluster calculation

Abstract

Full three-electron coupled cluster (CC) operators (triples) along with all singles and doubles are included in a valence universal multi-reference CC calculation to estimate the change in the correlation effect for ionization potential (IP) calculations. We study the vertical IPs of two typical systems, N 2 and CO, which go in the opposite direction, i.e., the results were worsened on inclusion of triples when working with relatively smaller basis. However, upon reaching the basis set saturation the expected trend in the results is observed and they are close within 0.1 eV to experimental values almost in every IP.