Free energy cost of forming an interface between a crystal and its frozen version

TL;DR

This study calculates the free energy cost of creating an interface between a crystal and a frozen wall with the same structure, revealing it varies with density and interaction type, and can be positive or negative.

Contribution

It introduces a thermodynamic integration method to quantify the free energy cost of crystal-wall interfaces, highlighting the effects of interaction potentials and density.

Findings

$\gamma$ increases with density for purely repulsive potentials.

$\gamma$ can be negative at low densities with attractive potentials.

The structure near the wall remains similar to the bulk crystal.

Abstract

Using a thermodynamic integration scheme, we compute the free energy cost per unit area, $\gamma$, of forming an interface between a crystal and a frozen structured wall, formed by particles frozen into the same equilibrium structure as the crystal. Even though the structure and potential energy of the crystalline phase in the vicinity of the wall is same as in the bulk, $\gamma$ has a non-zero value and increases with increasing density of the crystal and the wall. Investigating the effect of several interaction potentials between the particles, we observe a positive $\gamma$ at all crystalline densities if the potential is purely repulsive. For models with attractive interactions, such as the Lennard-Jones potential, a negative value for $\gamma$ is obtained at low densities.