Molecular Dynamics Simulations of Binary Sphere Mixtures

TL;DR

This paper uses advanced molecular dynamics simulations to study binary sphere mixtures with high size disparity, revealing structural insights and confirming some theoretical predictions while noting the absence of spontaneous crystallization.

Contribution

It introduces efficient algorithms for simulating highly size-dispersed particles and applies them to explore near-contact structures and correlations in binary sphere mixtures.

Findings

Confirmed qualitative predictions of large particle correlations.

Revealed additional near-contact structural insights.

Did not observe spontaneous crystal nucleation.

Abstract

Explicit simulations of fluid mixtures of highly size-dispersed particles are constrained by numerical challenges associated with identifying pair-interaction neighbors. Recent algorithmic developments have ameliorated these difficulties to an extent, permitting more efficient simulations of systems with many large and small particles of disperse sizes. We leverage these capabilities to perform molecular dynamics simulations of binary sphere mixtures with elastically stiff particles approaching the hard sphere limit and particle size ratios of up to 50, approaching the colloidal limit. The systems considered consist of 500 large particles and up to nearly 3.6 million small particles with total particle volume fractions up to 0.51. Our simulations confirm qualitative predictions for correlations between large particles previously obtained analytically and for simulations employing effective depletion interactions, but also reveal additional insights into the near-contact structure that result from the explicit treatment of the small particle solvent. No spontaneous crystal nucleation was observed during the simulations, suggesting that nucleation rates in the fluid-solid coexistence region are too small to observe crystal nucleation for feasible simulation system sizes and timescales.