Grand-Canonical Path Reweighting for Constant-Potential Langevin Dynamics.

Abstract

Constant-potential molecular dynamics provides an important framework for studying the structural, thermodynamic, and kinetic properties of electrochemical systems at a prescribed electrochemical potential, but independent simulations under different electrochemical conditions can be computationally demanding, particularly for rare-event kinetics. Here, we develop a trajectory reweighting framework based on extended-phase-space Langevin dynamics, in which the electron number Ne is treated as an additional dynamical degree of freedom and the nuclear and electronic degrees of freedom evolve within a unified Langevin framework. The proposed approach enables thermodynamic and kinetic properties at different electrochemical potentials to be obtained from a single ensemble of reference trajectories. We validate the method for the Volmer reaction at a Pt/water interface, where the reweighted trajectories reproduce both the thermodynamic properties and reaction rates obtained from direct dynamical simulations at the target electrochemical potential. The reweighting is performed entirely in postprocessing and introduces negligible additional computational cost. Furthermore, this dynamical reweighting approach can use well-sampled reference trajectories generated under conditions where the reaction proceeds more rapidly to estimate reaction rates under conditions where the reaction is slower.

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