On the accuracy of ionization potentials calculated by Green’s functions

A many-body Green’s function method is used to calculate vertical valence ionization potentials to high accuracy for the atoms and molecules Ne, N2, F2, CO2, P2, H2O, and H2S. Large basis sets including several sets of polarization functions are used in the calculations to reach the limit of the presently achievable accuracy for molecular systems. The maximum errors in the computed ionization potentials are 0.1 to 0.25 eV depending on the molecule and the basis set. The results are extremely stable, when large basis sets are used. Comparison with other methods is made.