Molecular dynamics simulation: a tool for exploration and discovery using simple models

TL;DR

This paper reviews how molecular dynamics simulations of simple models can reveal complex emergent phenomena across various fields, demonstrating their potential for exploration and discovery despite some limitations.

Contribution

It highlights the capability of MD simulations of simple models to uncover rich emergent behaviors in fluids, granular matter, and self-assembly processes, emphasizing their exploratory power.

Findings

Complex hydrodynamic phenomena can be observed and quantitatively matched in MD simulations.

Segregation phenomena in granular mixtures can be reproduced and understood through MD.

Reversible growth steps in self-assembly lead to high-yield, error-free structures.

Abstract

Emergent phenomena share the fascinating property of not being obvious consequences of the design of the system in which they appear. This characteristic is no less relevant when attempting to simulate such phenomena, given that the outcome is not always a foregone conclusion. The present survey focuses on several simple model systems that exhibit surprisingly rich emergent behavior, all studied by MD simulation. The examples are taken from the disparate fields of fluid dynamics, granular matter and supramolecular self-assembly. In studies of fluids modeled at the detailed microscopic level using discrete particles, the simulations demonstrate that complex hydrodynamic phenomena in rotating and convecting fluids, the Taylor-Couette and Rayleigh-B\'enard instabilities, can not only be observed within the limited length and time scales accessible to MD, but even quantitative agreement can be achieved. Simulation of highly counterintuitive segregation phenomena in granular mixtures, again using MD methods, but now augmented by forces producing damping and friction, leads to results that resemble experimentally observed axial and radial segregation in the case of a rotating cylinder, and to a novel form of horizontal segregation in a vertically vibrated layer. Finally, when modeling self-assembly processes analogous to the formation of the polyhedral shells that package spherical viruses, simulation of suitably shaped particles reveals the ability to produce complete, error-free assembly, and leads to the important general observation that reversible growth steps contribute to the high yield. While there are limitations to the MD approach, both computational and conceptual, the results offer a tantalizing hint of the kinds of phenomena that can be explored, and what might be discovered when sufficient resources are brought to bear on a problem.