## Koopmans' theorem

https://doi.org/10.1351/goldbook.K03411
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.
Source:
PAC, 1999, 71, 1919. (Glossary of terms used in theoretical organic chemistry) on page 1949 [Terms] [Paper]