Abstract
The application of Koopmans' theorem to open shell systems shows — compared with closed shell systems — an important difference: a mixture of one-electron-states of theN-electron system is needed for the quantum mechanical description of the (N – 1)-electron system. The ionization potentials are obtained as eigenvalues of a special matrix. Equations for the elements of thisI-matrix were derived which are applicable to systems having a doublet ground state. The derivation was carried out for the procedures developed by Roothaan, Kruglyak, McWeeny, Longuet-Higgins, and Pople and Nesbet using the density matrix formalism. First numerical calculations suggest that the effects which are taken into account in the exact form of Koopmans' theorem are important.
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Sauer, J., Jung, C. Konsequenzen des Koopmansschen Theorems in den Restricted Hartree Fock Methoden für open-shell-Systeme. Theoret. Chim. Acta 40, 129–141 (1975). https://doi.org/10.1007/BF01135884
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DOI: https://doi.org/10.1007/BF01135884
