Quantum Effects on the Free Energy of Ionic Aqueous Clusters Evaluated by Nonequilibrium Computational Methods

Abstract

Nonequilibrium simulation methods and rigid-body path-integral techniques are combined to estimate the relevance of protonic quantum effects in the free energy of ion-water clusters. The Crooks' fluctuation relation is used to quantitatively characterize the impact of quantum effects on the dissociation free energy of the paradigm I(-)(H(2)O)(5). By use of a rigorous smoothing procedure in the calculation of the work distributions, the effects are found to be about 11% and therefore non-negligible. Quantum effects on the potential of mean force of Na(+)(H(2)O)(12) were also evaluated using Jarzynski's work theorem for a reaction coordinate, and they were also found to be significant. The results suggest that quantization should play a significant role in the kinetics of ionic transport in aqueous environments.