Step Free Energies at Faceted Solid-Liquid Interfaces from Equilibrium Molecular Dynamics Simulations

TL;DR

This paper introduces a simulation-based method to calculate step free energies at faceted solid-liquid interfaces, demonstrating its application to silicon and highlighting the influence of interface geometry on coexistence temperatures.

Contribution

It presents a novel atomistic simulation approach using adiabatic trapping to determine step free energies at faceted interfaces, applicable to crystal growth and alloy casting.

Findings

Calculated coexistence temperature depends on interface geometry.

Island radius inversely relates to superheating, enabling free energy calculation.

Potential tends to crystallize silicon in wurtzite structure at low undercoolings.

Abstract

In this work a method is proposed for computing step free energies for faceted solid-liquid interfaces based on atomistic simulations. The method is demonstrated in an application to (111) interfaces in elemental Si, modeled with the classical Stillinger-Weber potential. The approach makes use of an adiabatic trapping procedure, and involves simulations of systems with coexisting solid and liquid phases separated by faceted interfaces containing islands with different sizes, for which the corresponding equilibrium temperatures are computed. We demonstrate that the calculated coexistence temperature is strongly affected by the geometry of the interface. We find that island radius is inversely proportional to superheating, allowing us to compute the step free energy by fitting simulation data within the formalism of classical nucleation theory. The approach outlined in this work paves the way to the calculation of step free energies relevant to the solidification of faceted crystals from liquid mixtures, as encountered in nanowire growth by the vapor-liquid-solid mechanism and in alloy casting. The present work also shows that at low undercoolings the Stillinger-Weber interatomic potential for Si tends to crystallize in the wurtzite, rather than the diamond-cubic structure.