Implications from Geometric Phase for Circulating Far Away Conical Intersection(s)

to elucidate this problem. The investigation leads to the conjecture that restricted Hartree-Fock solutions necessarily encounter a point of degeneracy along closed loops that encircle a (or an odd number of) conical intersection(s). Single-reference wave functions need to change character close to such points and cusps or discontinuities in a potential energy surface and multireference characters are a likely result, even when the energy gap between ground and excited states is large.