We study the appearance and properties of cluster crystals (solids in which the unit cell is occupied by a cluster of particles) with soft-core repulsive interactions in two different systems: i) an equilibrium system of Brownian particles in the overdamped limit, and ii) a system of self-propelled active particles. Despite the particles repel each other they spontaneously aggregate. We study this phenomenon at two levels of description: performing numerical simulations of the discrete particle dynamics, and by analysis of the corresponding Dean-Kawasaki equation for the macroscopic particle density. In the case of non-equilibrium active particles we show how self-propulsion deforms the clusters by depleting particle density inside, and for large speeds it melts the crystal.
Based on the papers: Delfau et al, Physical Review E 94, 042120 (1-13) (2016) Delfau, Lopez, Hernandez-Garcia, New Journal of Physics 19, 095001 (1-9) (2017)