Single-reference, size-extensive, non-iterative coupled-cluster approaches to bond breaking and biradicals
|Title||Single-reference, size-extensive, non-iterative coupled-cluster approaches to bond breaking and biradicals|
|Publication Type||Journal Article|
|Year of Publication||2006|
|Authors||Piecuch, P, Wloch, M, Gour, JR, Kinal, A|
|Journal||Chemical Physics Letters|
We propose the non-iterative, completely renormalized (CR) coupled-cluster (CC) approaches, including the CR-CC(2, 3) method which offers considerable improvements over the CCSD(T) approach without a significant increase in the computer effort. The CR-CC(2, 3) method, in which the CCSD (CC singles and doubles) energy is corrected for the effect of triples, is size extensive, competitive with CCSD(T) in calculations for non-degenerate states, and as accurate as the expensive CC approach with singles, doubles, and triples in the bond-breaking region. Calculations of the activation enthalpy for the thermal isomerizations of cyclopropane involving trimethylene suggest that CR-CC(2, 3) may be applicable to biradicals.