Towards an exact correlated orbital theory for electrons

This paper explores an alternative possibility to density functional theory (DFT) for developing an effective one-particle correlated orbital theory (COT), and an associated correlation orbital potential (COP), based upon insisting that the equations provide the exact principal ionization potentials (I) and electron affinities (A) for molecules. Elements of coupled-cluster theory and its equation-of-motion extensions are used to define a frequency independent self-energy, ΣCC, so that g = f + ΣCC, gφp = ωpφp, for orbitals, {φp}, where ωp = Ip for all the occupied levels and ωp = Ap for the unoccupied ones. The satisfaction of the COT equations provide consistency conditions on chosen approximations for two-particle interactions, which enable COT calculations to be done at the cost of a Hartree-Fock or DFT calculation.