W. Kurlancheek and M. Head-Gordon, “Violations of N-Representability from Spin-Unrestricted Orbitals in Mller-Plesset Perturbation Theory and Related Double-Hybrid Density Functional Theory,” Molecular Physics, Vol. 107, No. 8-12, 2009, pp. 1223-1232. doi10.1080/00268970902835637 - References - Scientific Research Publishing