Molecular applications of the intermediate Hamiltonian Fock-space coupled-cluster method for calculation of excitation energies

Abstract

The intermediate Hamiltonian Fock-space coupled-cluster (FS-CC) method with singles and doubles is applied to calculate vertical excitation energies (EEs) for some molecular systems. The calculations are performed for several small molecules, such as H2 O, N2, and CO, and for larger systems, such as C2 H4, C4 H6, and C6 H6. Due to the intermediate Hamiltonian formulation, which provides a robust computational scheme for solving the FS-CC equations, and the efficient factorization strategy, relatively large basis sets and model spaces are employed permitting a comparison of the calculated vertical EEs with the experimental data. © 2005 American Institute of Physics.