Phase behavior of a double-Gaussian fluid displaying water-like features

TL;DR

This study investigates the phase diagram of a double-Gaussian fluid with water-like features, revealing reentrant melting behavior and a high-pressure transition analogous to ice phase changes.

Contribution

It introduces a novel double-Gaussian potential model and maps its phase diagram, highlighting water-like anomalies and phase transitions not previously characterized.

Findings

Reentrant melting line persists in the phase diagram.

Water-like phase behavior observed at moderate pressures.

High-pressure transition to a more compact solid phase analogous to ice transitions.

Abstract

Pair potentials that are bounded at the origin provide an accurate description of the effective interaction for many systems of dissolved soft macromolecules (e.g., flexible dendrimers). Using numerical free-energy calculations, we reconstruct the equilibrium phase diagram of a system of particles interacting through a potential that brings together a Gaussian repulsion with a much weaker Gaussian attraction, close to the thermodynamic stability threshold. Compared to the purely-repulsive model, only the reentrant branch of the melting line survives, since for lower densities solidification is overridden by liquid-vapor separation. As a result, the phase diagram of the system recalls that of water up to moderate (i.e., a few tens MPa) pressures. Upon superimposing a suitable hard core on the double-Gaussian potential, a further transition to a more compact solid phase is induced at high pressure, which might be regarded as the analog of the ice I to ice III transition in water.