Extension of Koopmans’ theorem. I. Derivation

Abstract
It is shown that the spin orbitals that diagonalize the generalized Hartree−Fock potentials [Int. J. Quantum Chem. Symp., 8, 501 (1974)] for a correlated wavefunction, together with the corresponding orbital energies, give a natural extension of Koopmans’ theorem to correlated reference states.