Conical intersections induced by the Renner effect in polyatomic molecules

Characterizing and localizing electronic energy degeneracies is important for describing and controlling electronic energy flow in molecules. We show, using topological phase considerations, that the Renner effect in polyatomic molecules with more than three nuclei is necessarily accompanied by 'satellite' conical intersections. In these intersections the non-adiabatic coupling term is on average half an integer. We present ab initio results on the tetra-atomic radical cation C2H+2 to demonstrate the theory.