Cluster and reentrant anomalies of nearly Gaussian core particles

TL;DR

This study investigates the structural and dynamic anomalies in fluids of nearly Gaussian particles, revealing reentrant melting, clustering, and dimer formation through theory and simulations, with implications for soft matter systems.

Contribution

It introduces a detailed analysis of anomalies in ultrasoft particles with a generalized exponential potential, highlighting the coexistence of reentrant melting and clustering phenomena.

Findings

Identification of two new anomalies in structure and dynamics

Correlation between clustering and potential energy minima

Reentrant melting and clustering coexist for certain softness exponents

Abstract

We study through integral equation theory and numerical simulations the structure and dynamics of fluids composed of ultrasoft, nearly Gaussian particles. Namely, we explore the fluid phase diagram of a model in which particles interact via the generalized exponential potential u(r)=\epsilon exp[-(r/\sigma)^n], with a softness exponent n slightly larger than 2. In addition to the well-known anomaly associated to reentrant melting, the structure and dynamics of the fluid display two additional anomalies, which are visible in the isothermal variation of the structure factor and diffusivity. These features are correlated to the appearance of dimers in the fluid phase and to the subsequent modification of the cluster structure upon compression. We corroborate these results through an analysis of the local minima of the potential energy surface, in which clusters appear as much tighter conglomerates of particles. We find that reentrant melting and clustering coexist for softness exponents ranging from 2^+ up to values relevant for the description of amphiphilic dendrimers, i.e., n=3.