Coupled Cluster Theories for Strongly Correlated Molecular Systems

Abstract

The basic aspects of coupled cluster (CC) theories are reviewed from the perspective of its applicability to molecular systems with strong many-body correlation effects. In practice strong correlation refers to systems where the corresponding wavefunctions are characterized by multiconfigurational character corresponding to collective excitations from the reference function/functions. Several CC formalisms specifically designed to tackle these situations are discussed. These include single reference CC methodologies accounting for high-rank excitations and multireference CC approaches. Special attention is paid to non-iterative methods, which provide a widely accepted compromise between accuracy and numerical cost. We also discuss major theoretical and computational challenges which have to be addressed for the future developments of CC methodologies.