Coupled-cluster method in Fock space. II. Brueckner-Hartree-Fock method

Abstract

The generalized coupled-cluster (CC) method of the preceding paper is cast into the form of the Brueckner-Hartree-Fock (BHF) method. In this approach the model vacuum \ensuremath{\Phi} is optimized to become the maximum-overlap configuration for the reference eigenfunction \ensuremath{\Psi}. One of the approximation schemes of the preceding paper is applied to derive explicit algebraic equations which can be used for practical calculations of (approximate) energies of several states of a many-fermion system. These include the N-particle ground-state energy, energies of some (N-1)- and (N+1)-particle states, as well as energies of certain N-particle excited states. It is indicated that the numerical effort required in the present approach is comparable to that of the coupled-cluster singles and doubles (CCSD) method of Purvis and Bartlett [J. Chem. Phys. 76, 1910 (1982)].