Multireference Brillouin-Wigner Coupled Cluster Singles and Doubles (MRBWCCSD) and Multireference Doubles Configuration Interaction (MRD-CI) Calculations for the Bergman Cyclization Reaction

Abstract

We used the Bergman cyclization reaction of hex-3-ene-1,5-diyne to 1,4-didehydrobenzene (p-benzyne) as a benchmark system to assess the accuracy of recently developed multireference Brillouin-Wigner coupled cluster singles and doubles method (MRBWCCSD) in comparison with the multireference doubles configuration interaction (MRD-CI) calculations using the same geometry and basis set. Activation and reaction enthalpies were calculated. We found good agreement between experiment and theory at the MRCI+Q/CCSD(T) level of theory, provided a sufficiently large polarized basis set is used (cc-pVTZ). The MRBWCCSD theory gives results of a somewhat lower accuracy, presumably because of the absence of T3 clusters in the cluster expansion.