Treatment of symmetry in MO calculations. II. Numerical projection operators for molecular orbitals

This article describes the numerical application of projection operators to restore the symmetry of molecular orbitals in self‐consistent field (SCF) calculations when the symmetry is lost because of degeneracy or near degeneracy. The application of projection operators is particularly useful in cases of near degeneracies of three or more molecular orbitals, where it is difficult to find an effective algorithm for restoring the symmetry of molecular orbitals by orthonormal transformations.