Critical analysis of equations-of-motion—Green's function method: Ionization potentials of N2

Abstract

The X 2Σ+g, B 2Σ+u and A 2Πu ionization potentials of N2 are evaluated with the equations-of-motion (EOM)—Green's function method using four different basis sets and various forms of symmetrization. The importance of the inclusion of polarization functions is demonstrated as well as the necessity for having a basis which strikes a balance between those optimal for the neutral and ion states. With our best basis the calculated ionization potentials are within 0.35 eV of experimental values, and the results are of comparable accuracy to those obtained by Ermler with the same basis in a configuration interaction calculation with all singles and doubles with respect to the principal configuration for both the neutral and ion states.