How accurate is multireference coupled-cluster theory (in practice)?

Andreas Köhn
Institut für Theoretische Chemie, Universität Stuttgart, Stuttgart, Germany

Vendredi 9 Juin 2023, 11h00

The theoretical foundations of coupled-cluster theory and its multireference extension will be summarized. In particular, I will focus on the internally contracted formulation of multireference coupled-cluster theory (icMRCC) and the complications that arise in this variant. The accuracy of the approach with single and double excitations (icMRCCSD) will be discussed and its improvement by perturbative triple excitations. We will in particular look at extensive benchmark results from high-accuracy thermochemistry and try to gauge the merits and shortcomings of icMRCC in comparison with straightforward application of the single reference coupled-cluster hierarchy.