Non-adiabatic coupling terms NACTs

During the last few years major efforts were made to understand the features of the non-adiabatic coupling terms (NACTs) and their role in the theory of molecular physics (7-9). The NACTs owe their existence to the Born-Oppenheimer (BO) assumption which says that the fast moving electrons can be treated separately from the (assumed) slowly moving nuclei (70,77). The BO treatment seems to be somewhat artificial and somewhat too mathematical but... 

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