Application and Testing of Diagonal, Partial Third-Order Electron Propagator Approximations

Abstract

Ionization energies and electron affinities are among the most often sought thermochemical data. The importance of electron binding energies is reflected by their presence in a variety of thermodynamic arguments, including thermochemical cycles of acidity and basicity, complexation energies, and oxidation-reduction reactions. Many spectroscopic methods founded on the photoelectric effect, mass spectrometry, electron scattering, and other techniques measure ionization energies and electron affinities. The precision of these experiments in measuring transition energies often contrasts with the paucity of information they generate on accompanying molecular and ionic structures. Computational means of estimating ionization energies and electron affinities therefore provide indispensable corroborative information on structures, especially as the scope of thermochemical and spectroscopic measurements expands. Given the ubiquitous character of molecular orbital concepts in contemporary discourse on electronic structure, ionization energies and electron affinities provide valuable parameters for one-electron models of chemical bonding and spectra. Electron binding energies may be assigned to delocalized molecular orbitals and thereby provide measures of chemical reactivity. Notions of hardness and softness, electronegativity,