Variational transition state theory: Application to a symmetric exchange reaction in water

Abstract

Variational transition state theory (VTST) is applied for the first time to a chemical reaction in a liquid. The theory provides accurate estimates of reaction rates and leads to well defined microscopic friction functions. The structure of the optimized planar dividing surface provides insight into the range of solute–solvent interactions for which there is an appreciable effect on the reaction dynamics. The VTST method also allows for separation of the frictional effects of solvent translation, rotation, and stretch modes. The numerical cost is less than an analogous molecular dynamics reactive flux computation and the insight gained is greater.

Quantum harmonic transition state theory—Application to isomerization of stilbene in liquid ethane

“…This deficiency of the theory is well known, and many analytical and numerical methods have been developed to investigate the extent of the recrossing effect on the reaction rate and to analyze the role of solvent friction in reaction dynamics. 4 Usually, though, recrossing effects for a reasonably well chosen reaction coordinate are not large 7,8 and may be reduced by a systematic application of variational transition state theory to optimize the choice of reaction coordinate. 8 It is widely accepted that as long as the barrier height leading to reaction is large compared to k B T the norecrossing assumption does not lead to really serious errors in TST predictions.…”

Variational transition state theory for electron transfer reactions in solution

“…Analysis of the friction function, following the methods presented in Ref. 30, allows for differentiation between translational, vibrational, and rotational solvent effects on the ET dynamics. The utility of both approaches remains to be checked for some realistic ET simulations.…”

“…A realistic model based on such a reduced description can help in separating the dynamical and the equilibrium solvent contributions. Unlike many types of chemical reactions, in which there is usually an obvious choice of a reaction coordinate and there are well-defined procedures for computationally identifying the friction on this coordinate, 24,[26][27][28][29][30] in the ET case these concepts are more elusive. The solvent acts simultaneously as the source of activation and of dissipation, and as the major ingredient of the reaction coordinate.…”

A test of quantum transition state theory for a system with two degrees of freedom

“…5 The classical theory has been applied successfully to a large variety of systems. It is widely accepted that TST in its variational formulation 6,7 is quite accurate even in liquids, as long as the barrier height leading to reaction is large compared to k B T. [6][7][8][9] The main problem with TST is that it is inherently a classical theory as it is based on a simultaneous knowledge of the location of the reacting system and the sign of its momentum.…”