title: Performance of block correlated coupled cluster method with the CASSCF reference function for the prediction of activation barriers, spectroscopic constants in diatomic molecules, and singlet-triplet gaps in diradicals.
abstract: The spatial orbital formulations of block correlated coupled cluster (BCCC) theory with a general CASSCF reference function (CAS-BCCC in short) is derived and an efficient implementation of this approach at the four-block correlation level (abbreviated CAS-BCCC4) is reported. We have applied the CAS-BCCC4 approach to investigate energy barriers for several reactions (the ring-opening isomerization of the cyclopropyl radical, cyclobutene, cyclobutadiene, and bicyclo[3.1.0]hex-2-ene), spectroscopic constants in several multibond diatomic molecules (C(2), O(2), CO, and N(2)), and singlet-triplet gaps in two diradicals (trimethylenemethane and oxyallyl). A comparison of CAS-BCCC4 results with the experimental data or other theoretical estimates shows that the present approach can provide very satisfactory descriptions for all the studied systems.
authors.affiliation: School of Chemistry and Chemical Engineering, Key Laboratory of Mesoscopic Chemistry of Ministry of Education, Institute of Theoretical and Computational Chemistry, Nanjing University, Nanjing, 210093, PR China.
authors.forename: Jun
authors.initials: J
authors.lastname: Shen
authors.forename: Tao
authors.initials: T
authors.lastname: Fang
authors.forename: Shuhua
authors.initials: S
authors.lastname: Li
authors.forename: Yuansheng
authors.initials: Y
authors.lastname: Jiang