Koopmans’ theorem and its density-functional-theory analog assessed in evaluation of the red shift of vertical ionization potential upon complexation

Koopmans’ theorem and its density-functional-theory (DFT) analog with the statistical average of orbital (model) potentials (SAOP) are assessed in evaluation of the red shift of the first vertical ionization potential (VIP) of the fluoric acid in the prototype hydrogen-bonded complexes HF…HF and the H₂O…HF. The calculations point to the appreciable VIP red shift, which is stronger for the H₂O…HF. Comparison with the reference data shows that SAOP provides a good quality of both estimated VIP and its red shift upon complexation.