DETERMINATION OF BORN-OPPENHEIMER NUCLEAR MOTION WAVE-FUNCTIONS INCLUDING COMPLICATIONS DUE TO CONICAL INTERSECTIONS AND IDENTICAL NUCLEI

We show how the presence of a conical intersection in the adiabatic potential energy hypersurface can be handled by including a new vector potential in the nuclear-motion Schrödinger equation. We show how permutational symmetry of the total wave function with respect to interchange of nuclei can be enforced in the Born-Oppenheimer approximation both in the absence and the presence of conical intersections. The treatment of nuclear-motion wave functions in the presence of conical intersections and the treatment of nuclear-interchange symmetry in general both require careful consideration of the phases of the electronic and nuclear-motion wave functions, and this is discussed in detail. © 1979 American Institute of Physics.