Open-Boundary Hamiltonian adaptive resolution. From grand canonical to non-equilibrium molecular dynamics simulations

TL;DR

This paper introduces an open-boundary molecular dynamics method that models systems in contact with an infinite particle reservoir, enabling the simulation of non-equilibrium phenomena while conserving momentum.

Contribution

It develops a Hamiltonian adaptive resolution approach with an external potential and particle insertion/deletion algorithms to simulate open systems and non-equilibrium conditions.

Findings

Successfully simulates pressure-driven flow with realistic velocity profiles.

Maintains momentum conservation unlike other driven methods.

Can be applied to various out-of-equilibrium molecular systems.

Abstract

We propose an open-boundary molecular dynamics method in which an atomistic system is in contact with an infinite particle reservoir at constant temperature, volume and chemical potential. In practice, following the Hamiltonian adaptive resolution strategy, the system is partitioned into a domain of interest and a reservoir of non-interacting, ideal gas, particles. An external potential, applied only in the interfacial region, balances the excess chemical potential of the system. To ensure that the size of the reservoir is infinite, we introduce a particle insertion/deletion algorithm to control the density in the ideal gas region. We show that it is possible to study non-equilibrium phenomena with this open-boundary molecular dynamics method. To this aim, we consider a prototypical confined liquid under the influence of an external constant density gradient. The resulting pressure-driven flow across the atomistic system exhibits a velocity profile consistent with the corresponding solution of the Navier-Stokes equation. In contrast to available computational methods in which external forces drive the system far from equilibrium, this approach conserves momentum and closely resembles experimental conditions. The presented method can be used to study various direct and indirect out-of-equilibrium conditions in complex molecular systems.