Born-Oppenheimer approximation time-dependent molecular theory

In the framework of the Born-Oppenheimer approximation, radiationless transitions from one surface to another are impossible. (See, e.g., Michl and BonaCit -Koutecky, 1990.) It is therefore necessary to go beyond the Born-Oppenheimer approximation and to include the interaction between different electronic molecular states through the nuclear motion in order to be able to describe such transitions. Using the time-dependent perturbation theory for the rate constant of a transition between a pair of states one arrives at... 

Combining a microscopic electronic theory with molecular dynamics simulations in the Born-Oppenheimer approximation, Bennemann, Garcia, and Jeschke presented the first theoretical results for the ultrafast structural changes in the silver trimer [135]. They determined the timescale for the relaxation from the linear to a triangular structure initiated by a photodetachment process and showed that the time-dependent change of the ionization potential (IP) reflects in detail the internal degrees of freedom. 

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