Phase diagram of the Gaussian-core model

TL;DR

This study precisely maps the phase diagram of the Gaussian-core model, revealing complex phase transitions and reentrant melting behavior relevant to soft matter systems like star polymers.

Contribution

The paper provides the first detailed numerical phase diagram of the Gaussian-core model, including accurate free energy calculations and discovery of a fluid-BCC-FCC-BCC-fluid sequence.

Findings

Fluid-BCC-FCC triple point at about one third of maximum freezing temperature

Reentrant melting with phase sequence BCC-FCC-BCC in a narrow temperature range

Thermodynamic scenario partially revised based on new simulations

Abstract

We trace with unprecedented numerical accuracy the phase diagram of the Gaussian-core model, a classical system of point particles interacting via a Gaussian-shaped, purely repulsive potential. This model, which provides a reliable qualitative description of the thermal behavior of interpenetrable globular polymers, is known to exhibit a polymorphic FCC-BCC transition at low densities and reentrant melting at high densities. Extensive Monte Carlo simulations, carried out in conjunction with accurate calculations of the solid free energies, lead to a thermodynamic scenario that is partially modified with respect to previous knowledge. In particular, we find that: i) the fluid-BCC-FCC triple-point temperature is about one third of the maximum freezing temperature; ii) upon isothermal compression, the model exhibits a fluid-BCC-FCC-BCC-fluid sequence of phases in a narrow range of temperatures just above the triple point. We discuss these results in relation to the behavior of star-polymer solutions and of other softly repulsive systems.