Efficient Implementation of the Spin-Free Renormalized Internally-Contracted Multireference Coupled Cluster Theory
This paper reports an efficient, parallelized, spin-free implementation of the renormalized internally-contracted multireference coupled cluster with singles and doubles (RIC-MRCCSD) method within the ORCA software suite, which achieves computational costs comparable to single-reference CCSD while avoiding high-order reduced density matrices and demonstrating both scalability to large systems and accuracy comparable to various perturbation theories.