Ionization potential and electron affinity Koopmans rule

4 IONIZATION POTENTIAL AND ELECTRON AFFINITY (KOOPMANS RULE) 

The ionization potential of the molecule M is defined as the minimum energy needed for an electron to detach from the molecule. The electron affinity energy of the molecule M is defined as the minimum energy for an electron detachment from 

Electronic Motion in the Mean Field Atoms and Molecules 

Let us assume again naively, that during these operations the molecular orbitals and the orbital energies do not undergo any changes. In fact, of course, everything changes, and the computations should be repeated for each system separately (the same applies in the previous section for excitations). 

In our two-electron system, which is a model of any closed-shell molecule, the electron removal leaves the molecule with one electron only, and its energy has to be 

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Ionization potential and electron affinity (Koopmans rule)... 

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