On the ordering of the ionization energies in N2: A MC SCF study of near-degeneracy effects

Single configuration SCF wavefunctions yield poor results for the order and relative energies of low-lying icnic states of N₂. A multi-configurational SCF (MC SCF) model which takes account of the near degeneracy of a small number of strongly and weakly occupied orbitals corrects the errors of the SCF approach. MC SCF results for N₂ predict the correct ordering and give reasonably accurate results for the three lowest ionization potentials.