Pattern formation with repulsive soft-core interactions: discrete particle dynamics and Dean-Kawasaki equation

TL;DR

This paper investigates how repulsive soft-core particles can form clusters and periodic patterns in low dimensions, using simulations and analytical methods based on the Dean-Kawasaki equation.

Contribution

It provides a combined numerical and analytical study of clustering phenomena in low-dimensional soft-core particle systems, highlighting the role of the Dean-Kawasaki equation.

Findings

Deterministic Dean-Kawasaki equation accurately describes cluster formation.

Clustering results from the interplay of diffusion and inter-cluster forces.

Pattern-forming bifurcation analyzed with weakly nonlinear techniques.

Abstract

Brownian particles interacting via repulsive soft-core potentials can spontaneously aggregate, despite repelling each other, and form periodic crystals of particle clusters. We study this phenomenon in low-dimensional situations (one and two dimensions) at two levels of description: performing numerical simulations of the discrete particle dynamics, and by linear and nonlinear analysis of the corresponding Dean-Kawasaki equation for the macroscopic particle density. Restricting to low dimensions and neglecting fluctuation effects we gain analytical insight into the mechanisms of the instability leading to clustering which turn out to be the interplay between diffusion, the intracluster forces and the forces between neighboring clusters. We show that the deterministic part of the Dean-Kawasaki equation provides a good description of the particle dynamics, including width and shape of the clusters, in a wide range of parameters, and analyze with weakly nonlinear techniques the nature of the pattern-forming bifurcation in one and two dimensions. Finally, we briefly discuss the case of attractive forces.