Spectroscopic constants of single-bond diatomic molecules and singlet-triplet gaps of diradicals by the block-correlated coupled cluster theory

Jun Shen; Tao Fang; Weijie Hua; Shuhua Li

doi:10.1021/jp7118907

Spectroscopic constants of single-bond diatomic molecules and singlet-triplet gaps of diradicals by the block-correlated coupled cluster theory

J Phys Chem A. 2008 May 22;112(20):4703-9. doi: 10.1021/jp7118907.

Authors

Jun Shen¹, Tao Fang, Weijie Hua, Shuhua Li

Affiliation

¹ 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.

PMID: 18433169
DOI: 10.1021/jp7118907

Abstract

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.