Models for active particles: common features and differences

TL;DR

This paper compares various models of active particles with external field-dependent motility to understand how microscopic differences influence collective behavior in dilute and dense regimes.

Contribution

It systematically analyzes how different microscopic features of active particle models affect their collective dynamics, highlighting the importance of agent-specific properties.

Findings

Models show similar behavior in dilute regimes despite differences.

Dense regimes exhibit diverse collective behaviors based on model specifics.

Microscopic properties critically influence collective dynamics.

Abstract

Systems of active particles can show a large variety of collective behavior. In theory, two aspects determine the collective behavior: the model at the particle level and the parameter regime. While many studies consider a single model and study its parameter regime, here, we focus on the former aspect. Motivated by experiments that study dilute suspensions of Chlamydomonas reinhardtii in a self-generated oxygen gradient, we compare various models with external field-dependent motility to understand how the collective behavior changes between models. We vary the particle-particle interaction from no interactions to steric interactions, the particle shape from round disks to dumbbells, the self-propulsion mechanism from constant speed to rocking motion, and the particle's center of mass from the geometric center to off-center. We find that changes in the model of the active agents can lead to similar statistics in the dilute regime and different collective behavior in the dense regime. We conclude that active particle models do not easily generalize for different real active agents, but instead require a clear understanding of the agents' microscopic properties.