There are no unfilled shells in unrestricted Hartree-Fock theory.

Physical review letters

PubMedID: 10056037

Bach V, Lieb EH, Loss M, Solovej JP. There are no unfilled shells in unrestricted Hartree-Fock theory. Phys Rev Lett. 1994;72(19):2981-2983.
An abstract is not available