- A detailed numerical study has been made of the convergency of second-and approximate second-order multiconfigurational Hartree-Fock procedures. Calculations were performed on the excited 2p21S state of Be and on the lowest states of3g-1g1g+ 1g and3g symmetry in O2. The O2 calculations included all configurations that could be formed from doubly occupied core orbitals with eight electrons in the valence orbitals, 3g, 1u, 1-g and 3u. All second-order calculations converged in between 4 and 6 iterations even for a case where approximate second-order procedures did not converge. 1980 Taylor & Francis Group, LLC.