Block correlated coupled cluster method with a complete-active-space self-consistent-field reference function: the implementation for low-lying excited states.
Block correlated coupled cluster theory with the complete-active-space self-consistent-field reference function (CAS-BCCC) is generalized for low-lying electronic excited states. By truncating the cluster operator up to the four-block correlation level, the corresponding CAS-BCCC4 method for excited states has been efficiently implemented. The approach is applied to study the excited-state potential energy surfaces for HF and C(2) and to evaluate adiabatic or vertical excitation energies for CH(2), N(2), and trans-1,3-butadiene. The results are compared with those from the full configuration interaction, the internally contracted multireference configuration interaction with singles and doubles, the complete active space with second-order perturbation theory, and other theoretical methods (if available). The CAS-BCCC4 approach is found to provide high accuracy calculations for the low-lying excited states of the systems under study.
Fang
Tao
T
Key Laboratory of Mesoscopic Chemistry of Ministry of Education, Institute of Theoretical and Computational Chemistry, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093, People's Republic of China.
Shen
Jun
J
Li
Shuhua
S