A numerical study of the convergency of second and approximate second-order multiconfiguration Hartree-Fock procedures

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Abstract
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 2p 2 1 S state of Be and on the lowest states of 3Σ g -, 1δ g , 1Σ g +, 1Δ g and 3Δ g 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, 3σ g , 1π u , 1π g and 3σ u . All second-order calculations converged in between 4 and 6 iterations even for a case where approximate second-order procedures did not converge.