Failure of Born Oppenheimer approximation

[Yannick]

The intuition was derived from the mutual force between 1 electron and 1 nucleus. I would imagine if the nuclei interact mutually that this approximation doesn’t seem that valid anymore, especially if the mutual nuclei force don’t average out. Or when there is enough kinetic energy in the system for the nuclei to have an appreciable movement, say in an harmonic motion about a fixed center (if they would have too much kinetic energy then I guess its hard to define it as a solid ?)

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