Interfacial Free Energy: An Entropy Portent to Energy Changes

Abstract

Interfacial free energy is a critical quantity governing the behavior in processes such as crystal nucleation and growth, and there have been extensive efforts to measure or calculate this quantity for a variety of systems. Here, we show that profiles for the changes in energy and entropy across a solid/liquid interface can be extracted from molecular simulations. These smooth molecular level profiles can then be employed to estimate the free energy profile across a two-phase system. A distinctive feature of this profile is the presence of a peak in the free energy at the interface arising from the displacement of the change in entropy in advance of that of the energy. This concept is explicitly examined for the basal and prism interfaces of ice/water systems at the melting point and at undercooled conditions. The values obtained from this analysis for the interfacial free energy and thickness are in accord with previous estimates. The success of this approach demonstrates that microscopic details, captured in molecular level profiles, can be effectively linked to key thermodynamic quantities such as the interfacial free energy.