Demixing cascades in cluster crystals

TL;DR

This study investigates the phase transitions in cluster crystals with soft-core particles, revealing how the critical parameters of demixing cascades depend on particle softness and temperature, with implications for understanding clustering behavior.

Contribution

The paper introduces tailored Monte Carlo simulations to analyze demixing cascades in soft particle systems, providing detailed estimates of critical parameters across different softness levels.

Findings

Critical temperature and pressure vary non-monotonically with softness parameter n.

Cell model calculations confirm trends at zero temperature.

Clustering transitions are preempted by melting as n approaches 2+.

Abstract

In a cluster crystal, each lattice site is occupied by multiple soft-core particles. As the number density is increased at zero temperature, a `cascade' of isostructural phase transitions can occur between states whose site occupancy differs by unity. For low but finite temperature, each of these transitions terminates in a critical point. Using tailored Monte Carlo simulation techniques we have studied such demixing cascades in systems of soft particles interacting via potentials of the generalized exponential form $u(r)=\epsilon\exp[-(r/\sigma)^n]$. We have estimated the critical parameters of the first few transitions in the cascade as a function of the softness parameter $n$. The critical temperature and pressure exhibit non-monotonic behaviour as $n$ is varied, although the critical chemical potential remains monotonic. The trends for the pressure and chemical potential are confirmed by cell model calculations at zero temperature. As $n\to 2^+$, all the transitions that we have observed are preempted by melting although we cannot rule out that clustering transitions survive at high density.