Hexatic phase and water-like anomalies in a two-dimensional fluid of particles with a weakly softened core

TL;DR

This study investigates a two-dimensional particle system with soft-core interactions, revealing diverse melting behaviors, phase transitions, and water-like anomalies, contributing new insights into 2D fluid and solid phase phenomena.

Contribution

It demonstrates the existence of multiple crystal phases, distinct melting pathways, and water-like anomalies in a 2D soft-core particle model, highlighting novel phase behaviors.

Findings

Triangular solids melt into a hexatic fluid

Square solid transitions directly to isotropic fluid via first-order transition

Water-like anomalies are observed in the fluid phase

Abstract

We study a two-dimensional fluid of particles interacting through a spherically-symmetric and marginally soft two-body repulsion. This model can exist in three different crystal phases, one of them with square symmetry and the other two triangular. We show that, while the triangular solids first melt into a hexatic fluid, the square solid is directly transformed on heating into an isotropic fluid through a first-order transition, with no intermediate tetratic phase. In the low-pressure triangular and square crystals melting is reentrant provided the temperature is not too low, but without the necessity of two competing nearest-neighbor distances over a range of pressures. A whole spectrum of water-like fluid anomalies completes the picture for this model potential.