An improved dissipative coupling scheme for a system of Molecular Dynamics particles interacting with a Lattice Boltzmann fluid

TL;DR

This paper introduces an improved method for coupling Molecular Dynamics particles with a Lattice Boltzmann fluid, emphasizing a more stable and accurate implementation that conserves momentum more effectively.

Contribution

The paper proposes a new coupling scheme that updates fluid velocities more frequently, enhancing stability and accuracy with minimal computational overhead.

Findings

Frequent fluid velocity updates improve stability.

Momentum conservation is enhanced with the new scheme.

The method is computationally efficient.

Abstract

We consider the dissipative coupling between a stochastic Lattice Boltzmann (LB) fluid and a particle-based Molecular Dynamics (MD) system, as it was first introduced by Ahlrichs and D\"unweg (J. Chem. Phys. 111 (1999) 8225). The fluid velocity at the position of a particle is determined by interpolation, such that a Stokes friction force gives rise to an exchange of momentum between the particle and the surrounding fluid nodes. For efficiency reasons, the LB time step is chosen as a multiple of the MD time step, such that the MD system is updated more frequently than the LB fluid. In this situation, there are different ways to implement the coupling: Either the fluid velocity at the surrounding nodes is only updated every LB time step, or it is updated every MD step. It is demonstrated that the latter choice, which enforces momentum conservation on a significantly shorter time scale, is clearly superior in terms of stability and accuracy, and nevertheless only marginally slower in terms of execution speed. The second variant is therefore the recommended implementation.