The solid-liquid interfacial free energy out of equilibrium

TL;DR

This paper develops a new framework and simulation method to accurately define and measure the solid-liquid interfacial free energy under out-of-equilibrium conditions, revealing complex temperature dependence.

Contribution

It introduces a novel approach connecting atomistic and thermodynamic descriptions, enabling direct evaluation of interfacial free energy away from melting point.

Findings

Interfacial free energy varies non-linearly with temperature.

The new method allows reversible creation and destruction of interfaces.

Results challenge the assumption of constant interfacial free energy slope.

Abstract

The properties of the interface between solid and melt are key to solidification and melting, as the interfacial free energy introduces a kinetic barrier to phase transitions. This makes solidification happen below the melting temperature, in out-of-equilibrium conditions at which the interfacial free energy is ill-defined. Here we draw a connection between the atomistic description of a diffuse solid- liquid interface and its thermodynamic characterization. This framework resolves the ambiguities in defining the solid-liquid interfacial free energy above and below the melting temperature. In addition, we introduce a simulation protocol that allows solid-liquid interfaces to be reversibly created and destroyed at conditions relevant for experiments. We directly evaluate the value of the interfacial free energy away from the melting point for a simple but realistic atomic potential, and find a more complex temperature dependence than the constant positive slope that has been generally assumed based on phenomenological considerations and that has been used to interpret experiments. This methodology could be easily extended to the study of other phase transitions, from condensation to precipitation. Our analysis can help reconcile the textbook picture of classical nucleation theory with the growing body of atomistic studies and mesoscale models of solidification.