Koopmans' theorem

Directly relates experimental @I03183@ potentials with energy levels of molecular orbitals. The theorem states that the @I03208@ required to remove an electron from the orbital \(\Psi _{\text{i}}\) is given by the negative value of the energy of the orbital, \(-\varepsilon _{\text{i}}\), as calculated within the @H02747@–Fock approximation. The theorem is not applied to localized molecular orbitals, which are not eigenfunctions of the effective hamiltonian.
PAC, 1999, 71, 1919. (Glossary of terms used in theoretical organic chemistry) on page 1949 [Terms] [Paper]