Spectroscopic constants of single-bond diatomic molecules and singlet-triplet gaps of diradicals by the block-correlated coupled cluster theory.
The spatial orbital formulations of block-correlated coupled cluster (BCCC) theory with a complete active-space self-consistent-field (CASSCF) reference function and its efficient implementation is presented. In the present implementation, the cluster operator is truncated to the four-block correlation level, and the CASSCF(2,2) reference function is assumed (thus, the method is abbreviated as CAS-BCCC4). We have applied this method to investigate the spectroscopic constants in seven single-bond diatomic molecules (LiH, HF, HCl, Li(2), F(2), ClF, and Cl(2)) and the singlet-triplet gaps in a series of typical diradicals, including carbon, oxygen, and silicon atoms, methylene (CH(2)) and its isovalent species (NH(2)(+), SiH(2), and PH(2)(+)), and three benzyne isomers. A comparison of our results with the experimental data or other theoretical estimates shows that the present approach can provide quantitative descriptions for all of the studied systems.
Shen
Jun
J
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, People's Republic of China.
Fang
Tao
T
Hua
Weijie
W
Li
Shuhua
S