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

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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 Φ is optimized to become the maximum-overlap configuration for the reference eigenfunction Ψ. 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)].