On methods for converging open-shell Hartree-Fock wave-functions

Abstract
The ‘level-shifting’ technique of Saunders and Hillier is extended so as to allow guaranteed convergence of the restricted Hartree-Fock energy for many commonly found open-shell configurations. The proposed energy minimization scheme is compared with other procedures due to McWeeny, Roothaan and Segal. A test case calculation on the 2Σ+ ground state of boron oxide is described.