Unified coupling operator for ‘non-Roothaan’ open-shell states of high-symmetry molecules

The self-consistency approach for the calculation of open-shell states of high-symmetry molecules within the symmetry-restricted Hartree-Fock method is presented. The approach is applicable for terms of any type and allows the use of an arbitrary set of energy-integral coupling coefficients satisfying only the fundamental energy relation without any additional restrictions. The unified coupling operator is constructed on the basis of the pseudosecular method providing effective convergence to the energy minimum. The applicability of the proposed procedure is illustrated by calculations performed in a simple model of the icosahedral fullerene molecule.