Intersections and Symmetry

Symmetry-Required Conical Intersections The Jahn-Teller Effect 

Most molecular systems in nature have little or no symmetry, and it is in these systems that accidental conical intersections often exist. Locating accidental points of degeneracy is more difficult than the previous cases because there is no symmetry that can be used for guidance. This difficulty, along with the misinterpretation of the noncrossing rule, delayed the appreciation of accidental conical intersections. One of the early cases where accidental 

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