Reactive path ensembles within nonequilibrium steady-states

TL;DR

This paper explores how reactive processes in nonequilibrium steady states differ from equilibrium, using variational path sampling to analyze energy effects, persistent currents, and new reaction pathways.

Contribution

It introduces a variational path sampling method to study nonequilibrium reactive events without relying on equilibrium assumptions.

Findings

Energy injection enhances rare event rates.

Nonequilibrium paths deviate from gradient paths due to persistent currents.

Unstable states in equilibrium can be stabilized kinetically out of equilibrium.

Abstract

The modern theory of rare events is grounded in near equilibrium ideas, however many systems of modern interest are sufficiently far from equilibrium that traditional approaches do not apply. Using the recently developed variational path sampling methodology, we study systems evolving within nonequilibrium steady states to elucidate how reactive processes are altered away from equilibrium. Variational path sampling provides access to ensembles of reactive events, and a means of quantifying the relative importance of each dynamical degree of freedom in such processes. With it, we have studied the conformational change of a solute in an active bath. We illustrate how energy injection generically enhances the rates of rare events, even when energy is not directed into specific reactive modes. By studying the folding and unfolding transitions of a grafted polymer under shear, we illustrate how nonequilibrium reactive processes do not follow gradient paths due to the emergence of persistent currents. The breaking of detailed balance allows for the mechanisms of forward and backward reactions to be distinct, enabling novel pathways to be explored and designed, and states unstable in equilibrium to become stabilized kinetically away from it. The analysis presented in this work establishes some basic principles for nonequilibrium reactive events, and is made possible by the use of a numerical method that does not invoke proximity to equilibrium or requires strong prior assumptions about the mechanism of reaction.