Phase diagram of Kob-Andersen type binary Lennard-Jones mixtures

TL;DR

This study maps the phase diagram of the Kob-Andersen binary Lennard-Jones mixture, revealing crystallization behaviors, melting temperatures, and phase stability across different compositions and pressures.

Contribution

It provides the first detailed thermodynamic phase diagram for KA-type mixtures up to 50% B particles, including melting points and stable crystal structures.

Findings

Melting temperature of standard KA system is 1.028(3) in LJ units.

Crystallization into FCC and CsCl structures depends on B particle concentration.

Eutectic point around 26% B particles with stable PuBr3 structure.

Abstract

The binary Kob-Andersen (KA) Lennard-Jones mixture is the standard model for computational studies of viscous liquids and the glass transition. For very long simulations the viscous KA system crystallizes, however, by phase separating into a pure A particle phase forming an FCC crystal. We present the thermodynamic phase diagram for KA-type mixtures consisting of up to 50\% small (B) particles showing, in particular, that the melting temperature of the standard KA system at liquid density $1.2$ is $1.028(3)$ in A particle Lennard-Jones units. At large B particle concentrations the system crystallizes into the CsCl crystal structure. The eutectic corresponding to the FCC and CsCl structures is cut-off in a narrow interval of B particle concentrations around 26\% at which the bipyramidal orthorhombic ${\rm PuBr_3}$ structure is the thermodynamically stable phase. The melting temperature's variation with B particle concentration at two other pressures, as well as at the constant density $1.2$, is estimated from the simulations at pressure $10.19$ using isomorph theory. Our data demonstrate approximate identity between the melting temperature and the onset temperature below which viscous dynamics appears. Finally, the nature of the solid-liquid interface is briefly discussed.