The Raspberry Model for Hydrodynamic Interactions Revisited. II. The Effect of Confinement

TL;DR

This paper evaluates and improves the raspberry model's accuracy in simulating hydrodynamic interactions of colloidal particles under confinement, demonstrating that internal coupling points enhance its precision in confined geometries.

Contribution

The study extends the raspberry model to confined geometries, showing that internal coupling points improve the accuracy of hydrodynamic interaction simulations.

Findings

Adding internal coupling points corrects mobility discrepancies.

The model accurately reproduces interactions up to one LB lattice spacing.

Comparison with theoretical and finite-element results validates the improvements.

Abstract

The so-called 'raspberry' model refers to the hybrid lattice-Boltzmann (LB) and Langevin molecular dynamics scheme for simulating the dynamics of suspensions of colloidal particles, originally developed by [V. Lobaskin and B. D\"unweg, New J. Phys. 6, 54 (2004)], wherein discrete surface points are used to achieve fluid-particle coupling. In this paper, we present a follow up to our study of the effectiveness of the raspberry model in reproducing hydrodynamic interactions in the Stokes regime for spheres arranged in a simple-cubic crystal [L. Fischer, et al., J. Chem. Phys. 143, 084108 (2015)]. Here, we consider the accuracy with which the raspberry model is able to reproduce such interactions for particles confined between two parallel plates. To this end, we compare our LB simulation results to established theoretical expressions and finite-element calculations. We show that there is a discrepancy between the translational and rotational mobility when only surface coupling points are used, as also found in Part I of our joint publication. We demonstrate that adding internal coupling points to the raspberry, can be used to correct said discrepancy in confining geometries as well. Finally, we show that the raspberry model accurately reproduces hydrodynamic interactions between a spherical colloid and planar walls up to roughly one LB lattice spacing.