Thermal and Athermal Swarms of Self-Propelled Particles

TL;DR

This study explores the diverse structures of self-propelled particle swarms in three dimensions, revealing how parameters and initial conditions influence their formation and reconfiguration, with implications for nonequilibrium self-assembly.

Contribution

It provides a comprehensive phase diagram of self-propelled Morse particle swarms and examines the effects of thermal noise and initial conditions on swarm structures.

Findings

Identification of various swarm shapes and coexistence of structures.

Thermal noise can be used to reconfigure swarm structures.

Initial conditions bias the probability of swarm formation.

Abstract

Swarms of self-propelled particles exhibit complex behavior that can arise from simple models, with large changes in swarm behavior resulting from small changes in model parameters. We investigate the steady-state swarms formed by self-propelled Morse particles in three dimensions using molecular dynamics simulations optimized for GPUs. We find a variety of swarms of different overall shape assemble spontaneously and that for certain Morse potential parameters coexisting structures are observed. We report a rich "phase diagram" of athermal swarm structures observed across a broad range of interaction parameters. Unlike the structures formed in equilibrium self-assembly, we find that the probability of forming a self-propelled swarm can be biased by the choice of initial conditions. We investigate how thermal noise influences swarm formation and demonstrate ways it can be exploited to reconfigure one swarm into another. Our findings validate and extend previous observations of self-propelled Morse swarms and highlight open questions for predictive theories of nonequilibrium self-assembly.