The structure and dynamics of aqueous protons play fundamental roles in many areas of chemistry, biology, and physics. The aqueous proton displays an anomalously large diffusion coefficient that is up to 7 times that of similarly sized cations. There is general consensus that the proton achieves its high diffusion through the Grotthuss mechanism, whereby protons hop from one molecule to the next. Although much work has been done to understand the details of this mechanism, one aspect that has received relatively little attention is the model used to extract the timescale of the mechanism from experimental results. Based upon a large set of ab initio molecular dynamics trajectories, totaling more than 10 ns in simulation time, we show that the commonly used simple random walk model is not generally valid for the Grotthuss mechanism. Instead, we propose the use of a correlated random walk model for the interpretation of the experimental results and show how this model points to a timescale 2-3 times faster than was previously anticipated.

Correlated dynamics and random walks in aqueous proton diffusion

2019 Spring National Meeting

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