A parallel algorithm for implicit depletant simulations

TL;DR

This paper introduces a parallel algorithm for efficiently simulating many-body depletion interactions in colloids by integrating out depletants, validated on CPUs and GPUs, revealing novel cluster phases.

Contribution

The paper presents a novel parallel algorithm that implicitly simulates depletion interactions, significantly improving speed and enabling new insights into colloid phase behavior.

Findings

Discovery of novel cluster phases with hemispheres forming spheres and lattices

Algorithm is faster than explicit depletant tracking methods for certain densities

Enables simulation of fluid-solid transitions in colloidal systems

Abstract

We present an algorithm to simulate the many-body depletion interaction between anisotropic colloids in an implicit way, integrating out the degrees of freedom of the depletants, which we treat as an ideal gas. Because the depletant particles are statistically independent and the depletion interaction is short-ranged, depletants are randomly inserted in parallel into the excluded volume surrounding a single translated and/or rotated colloid. A configurational bias scheme is used to enhance the acceptance rate. The method is validated and benchmarked both on multi-core CPUs and graphics processing units (GPUs) for the case of hard spheres, hemispheres and discoids. With depletants, we report novel cluster phases, in which hemispheres first assemble into spheres, which then form ordered hcp/fcc lattices. The method is significantly faster than any method without cluster moves and that tracks depletants explicitly, for systems of colloid packing fraction $\phi_c<0.50$, and additionally enables simulation of the fluid-solid transition.