A Local Pair Natural Orbital-Based Multireference Mukherjee's Coupled Cluster Method

This paper reports the development of a local variant ofMukherjee's state-specific multireference coupled cluster method based on the pair natural orbital approach (LPNO-MkCC). The current implementation is restricted to single and double excitations. The performance of the LPNO-MkCCSD method was tested- On calculations of naphthyne isomers, tetramethyleneethane, and beta-carotene molecules. The results show that 99:7-99.8% of correlation energy was recovered with respect to the MkCC method based on canonical orbitals. Moreover, the errors of relative energies between different isomers or along a potential energy curve (with respect to the canonical method) are below 0.4 kcal/mol, safely within the chemical accuracy. The computational efficiency of 100 our implementation of LPNO-MkCCSD in the rORCA program allows calculation of the beta-carotene molecule (96 atoms and 1984 basis functions) on a single CPU core.