Cluster glasses of ultrasoft particles

TL;DR

This study uses molecular dynamics simulations to explore the formation and dynamics of disordered cluster phases and cluster glasses in dense fluids of ultrasoft, penetrable particles, revealing microsegregation and activated relaxation.

Contribution

It demonstrates the formation of disordered cluster phases and cluster glasses in ultrasoft particle systems with dispersity, highlighting the role of microscopic dynamics on transport properties.

Findings

Disordered cluster phases form via a smooth crossover.

Cluster glass transition involves slowed cluster motion and activated particle hopping.

Microsegregation of particle sizes occurs within clusters.

Abstract

We present molecular dynamics (MD) simulations results for dense fluids of ultrasoft, fully-penetrable particles. These are a binary mixture and a polydisperse system of particles interacting via the generalized exponential model, which is known to yield cluster crystal phases for the corresponding monodisperse systems. Because of the dispersity in the particle size, the systems investigated in this work do not crystallize and form disordered cluster phases. The clustering transition appears as a smooth crossover to a regime in which particles are mostly located in clusters, isolated particles being infrequent. The analysis of the internal cluster structure reveals microsegregation of the big and small particles, with a strong homo-coordination in the binary mixture. Upon further lowering the temperature below the clustering transition, the motion of the clusters' centers-of-mass slows down dramatically, giving way to a cluster glass transition. In the cluster glass, the diffusivities remain finite and display an activated temperature dependence, indicating that relaxation in the cluster glass occurs via particle hopping in a nearly arrested matrix of clusters. Finally we discuss the influence of the microscopic dynamics on the transport properties by comparing the MD results with Monte Carlo simulations.