FOCK-SPACE COUPLED-CLUSTER METHOD IN THE INTERMEDIATE HAMILTONIAN-FORMULATION - MODEL WITH SINGLES AND DOUBLES

The intermediate Hamiltonian technique is applied to reformulate the F ock-space coupled-cluster (FSCC) method with singles and doubles. A ve rsion of FSCC designated to direct calculation of excitation energies is considered. The presented scheme offers several advantages over tho se used so far;like simplification of the equations, smooth convergenc e, and the possibility of one-root calculation. Results of some illust rative numerical examples are also shown where comparison with other m ethods as well as with the full configuration interaction results is a vailable. (C) 1998 American Institute of Physics. [S0021-9606(98)30122 -1].