A reliable and inexpensive method for calculating ionization potentials and electron affinities of radicals and molecules

Abstract

The ionization potentials and electron affinities of a variety of organic radicals and closed-shell molecules have been calculated with the outer valence Green's function (OVGF) technique, coupled with semiempirical MNDO, AM1 and PM3 calculations. The calculations cover a wide range of energies > 11 eV in a variety of radicals and molecules. It is found that the OVGF method gives significantly better agreement with the experimental data than do results obtained with semiempirical calculations using Koopmans' theorem. Of the three semiempirical methods tested (MNDO, AM1, PM3) the OVGF(AM1) method gives the best agreement with experiment (e.g., for the vertical ionization potentials of 38 different organic radicals the mean deviation between experimental data and theoretical values is only 0.35 eV), and thereby can serve as a routine method for the calculation of the above-mentioned molecular properties of a variety of species.