Phase diagram of softly repulsive systems: The Gaussian and inverse-power-law potentials

TL;DR

This study maps the phase diagrams of Gaussian and inverse-power-law repulsive potentials using advanced free-energy methods, revealing similarities and phase behaviors like reentrant BCC phases and the influence of softness on phase coexistence.

Contribution

It provides detailed phase diagrams for these models and links their features to the softness of the interaction potential, using state-of-the-art computational techniques.

Findings

Reentrant BCC phase in Gaussian-core model above the triple point.

Phase coexistence line between BCC and FCC varies with the power exponent n.

Thermodynamic properties are similar despite different behaviors at short distances.

Abstract

We redraw, using state-of-the-art methods for free-energy calculations, the phase diagrams of two reference models for the liquid state: the Gaussian and inverse-power-law repulsive potentials. Notwithstanding the different behavior of the two potentials for vanishing interparticle distances, their thermodynamic properties are similar in a range of densities and temperatures, being ruled by the competition between the body-centered-cubic (BCC) and face-centered-cubic (FCC) crystalline structures and the fluid phase. We confirm the existence of a reentrant BCC phase in the phase diagram of the Gaussian-core model, just above the triple point. We also trace the BCC-FCC coexistence line of the inverse-power-law model as a function of the power exponent $n$ and relate the common features in the phase diagrams of such systems to the softness degree of the interaction.