Conserving the linear momentum in stochastic dynamics: Dissipative particle dynamics as a general strategy to achieve local thermostatization in molecular dynamics simulations

Abstract

Stochastic dynamics is a widely employed strategy to achieve local thermostatization in molecular dynamics simulation studies; however, it suffers from an inherent violation of momentum conservation. Although this short-coming has little impact on structural and short-time dynamic properties, it can be shown that dynamics in the long-time limit such as diffusion is strongly dependent on the respective thermostat setting. Application of the methodically similar dissipative particle dynamics (DPD) provides a simple, effective strategy to ensure the advantages of local, stochastic thermostatization while at the same time the linear momentum of the system remains conserved. In this work, the key parameters to employ the DPD thermostats in the framework of periodic boundary conditions are investigated, in particular the dependence of the system properties on the size of the DPD-region as well as the treatment of forces near the cutoff. Structural and dynamical data for light and heavy water as well as a Lennard-Jones fluid have been compared to simulations executed via stochastic dynamics as well as via use of the widely employed Nose-Hoover chain and Berendsen thermostats. It is demonstrated that a small size of the DPD region is sufficient to achieve local thermalization, while at the same time artifacts in the self-diffusion characteristic for stochastic dynamics are eliminated. © 2016 Wiley Periodicals, Inc.

A Thermostat‐Consistent Fully Coupled Molecular Dynamics—Generalized Fluctuating Hydrodynamics Model

“…Indeed, the forcing term in Equation (24) incorporates the fluctuating hydrodynamics force , which corresponds to a gradient of the corresponding stochastic Reynolds stress (5), and which becomes partially balanced by the Langevin damping. However, in comparison with the stochastic thermostat model driven by Brownian dynamics, [ 33 ] the stochastic hydrodynamic term of the suggested model is only active in the hybrid part of the domain () while the Langevin damping vanishes in the particle‐free part of the domain (see Equation (17a)). Furthermore, the produced dissipation does not violate the total momentum conservation because of the two‐phase flow analogy formulation, where the sources and the sinks of the two phases (Equations (3) and (4)) cancel out for the mixture momentum, which corresponds to and .…”