Decay of mixing with coherence switching

In their studies of nonadiabatic dynamics in condensed phase, Rossky and his colleagues emphasized the role of stochastic perturbations that actually decohere the surroimded quantum states (solute state) [327, 468]. This is one of the most significant phenomena in the dynamics of open systems. 

Chemical Theory Beyond the Born-Oppenheimer Paradigm 

On the other hand, in nonadiabatic dynamics within a single molecule or isolated molecular reaction system, it is Hack, Jasper and Truhlar [197, 452, 509, 515] who first devised how to implement the decay of electronic state coherence, or decay of mixing, into the nuclear dynamics of individual path, thus bringing about the notion of non-Born-Oppenheimer path in an explicit manner. 

It is interesting to compare the Truhlar non-Born-Oppenheimer path with those expected to emerge from the mechanics of Pechukas, Eq. (4.31). In the latter, a non-Born-Oppenheimer path, if it indeed exists, starts from 

Decoherence is an essential concept appearing in a system in which a quantum subsystem contacts classical subsystem(s) in one way or another. As is widely recognized, the SET cannot describe this dynamics since there is no mechanism in it to switch off the electronic coherence along the nuclear path. The decoherence problem is critically important not only in our nonadiabatic dynamics but in other contemporary science such as spin-Boson dynamics in quantum computation theory and more extensively a quantum theory in open (dissipative) systems [147]. The decoherence problem is also critical to chaos induced by nonadiabatic djmamics [136, 137,182, 453, 454]. Therefore, in the rest of this section, we pay deeper attention to the aspect of the effect of electronic state decoherence strongly coupled with the relevant nuclear motion. A review about the notion of decoherence related to quantum mechanical measmement theory is found in the papers by Rossky et al. [53]. 

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