We formulate an effective independent particle model where the effective Hamiltonian is composed of the Fock operator and a correlation potential.Within the model the kinetic energy and the exchange energy can be expressed exactly leaving the correlation energy functional as the remaining unknown.Our efforts concentrate on finding a correlation potential such that exact ionization potentials and electron affinities can be reproduced as orbital energies.The equation-of-motion coupled-cluster approach enables us to define an effective Hamiltonian from which a correlation potential can be extracted.We also make the connection to electron propagator theory.The disadvantage of the latter is the inherit energy dependence of the potential resulting in a different Hamiltonian for each orbital.Alternatively,the Fock space coupled-cluster approach employs an effective Hamiltonian which is energy independent and universal for all orbitals.A correlation potential is extracted which yields the exact ionization potentials and electron affinities and a set of associated molecular orbitals.We also describe the close relationship to Brueckner theory.
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