Correlated one-particle method: Numerical results

Intermediate Hamiltonian Fock-space multireference coupled-cluster method with full triples for calculation of excitation energies

The intermediate Hamiltonian multireference coupled-cluster (CC) method with singles, doubles, and triples within the excited (1,1) sector of Fock space (FS) is implemented and formulated to calculate excitation energies (EEs). Due to the intermediate Hamiltonian formulation, which provides a robust computational scheme for solving the FS-CC equations, coupled to an efficient factorization strategy, relatively large basis sets and model spaces are employed permitting basis set converged comparisons of the calculated vertical EEs, which can be compared to the experimental data for the N(2) and CO molecules. The issue of charge-transfer separability is also addressed.

Investigation of a localised second-order Brueckner correlation method

Local second-order Brueckner correlation potentials have been derived from their non-local counterparts by starting from the assumption that the orbitals generated by these potentials are the same. The structure of the local correlation potentials and its components have been analysed for the neon atom and a range of small molecules, namely HF, HCl, H(2)O, CO and ethyne. The orbitals from the local Brueckner correlation potentials yield first-order electric molecular properties which are close to those inferred from second-order Møller-Plesset theory and Brueckner coupled cluster doubles with perturbative triples.