On multiple solutions of the Fock-space coupled-cluster method

Intermediate Hamiltonian techniques are used to investigate the problem of multiple solutions of the Fock-space coupled-cluster methods. Two intermediate Hamiltonian schemes are presented, based upon similarity transformations that unlike the wave operator formalism allow for following the complete eigenvalue problem. Solutions of the standard effective Hamiltonian formulation that requires iterative approaches to solve the equations are equivalently given by diagonalization of the intermediate Hamiltonian matrix representations. This procedure provides a systematic way of obtaining all possible solutions of the effective Hamiltonian scheme in all sectors higher than the lowest one.