Entropic bottlenecks

A different strategy to approach such problems is to search for the dynamical bottlenecks through which the system passes during a transition between metastable states. If the dynamics of the system is dominated by energetic effects (as opposed to entropic effects), such bottlenecks can be identified with saddle points in the potential energy surface. In this case, saddle points are transition states, activated states from which the system can access different stable states through small fluctuations. Comparing stable states with transition states one can often infer the mechanism of the reaction. Reaction rate constants, which are very important because they are directly comparable to... 

The location of the GTS corresponding to this minimum flux can be interpreted as a dynamical bottleneck to the reaction, in that it includes both entropic effects (associated with the ratio of the partition functions for the GTS and the reactants) and zero-point energy effects as well as the energetic effects in Vj ep(s)- In addition, since this minimum corresponds to a maximum in the generalized standard-state free energy change for the formation of the GTS at s from the reactants, AG (T,s) [42,44,47,78,79], the CVT approach can also be applied to reactions in which V, Ep(s) does not exhibit a barrier between the reactants and products. 

Entropic Effects on the Dynamical Bottleneck Location and Tunneling Contributions for C2hl4 -F H — C2H5. Variable Scaling of External Correlation Energy for... 

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