Entropic Origin of the Attenuated Width of the Ice-Water Interface

The solid-liquid interface of water is similar to 50% narrower (or thinner) than that of argon. With the help of molecular dynamics simulations, we compare two water models, namely, TIP4P/ice and mW, with Lennard-Jones argon to understand the origin of this difference. We find that the sharpness of the ice-water interface is partly entropic in origin. The sharp drop in structural order from the crystalline to the liquid phase of water is assisted by a large increase in rotational entropy. We find that this change is strongly correlated to the number of hydrogen bond (HB) defects at the interface. The concentration of HB defects has earlier been correlated with entropy. We also find that the interfacial width is dependent on the order parameter chosen to define the interface. However, it always remains wider for the argon interface than that for water.