Koopmans' theorem

https://doi.org/10.1351/goldbook.K03411
Directly relates experimental ionization potentials with energy levels of molecular orbitals. The theorem states that the ionization potential required to remove an electron from the orbital Ψi is given by the negative value of the energy of the orbital, −εi, as calculated within the Hartree–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]
Citation: 'Koopmans' theorem' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. https://doi.org/10.1351/goldbook.K03411 RIS BibTex EndNote
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Last revised: February 24, 2014