Surface entropy of liquids via a direct Monte Carlo approach: Application to liquid Si

We present two methods for a direct Monte Carlo evaluation of the surface entropy ${\mathit{S}}_{\mathit{s}}$ of a liquid interacting by specified, volume-independent potentials. The first method is based on an application of the approach of Ferrenberg and Swendsen [Phys. Rev. Lett. 61, 2635 (1988); 63, 1195 (1989)] to Monte Carlo simulations at two different temperatures; it gives much more reliable results for ${\mathit{S}}_{\mathit{s}}$ in liquid Si than previous calculations based on numerical differentiation. The second method expresses the surface entropy directly as a canonical average at fixed temperature.