where P F and P S are the probabilities of finding a fluid particle in the solid or vapour interfacial region (defined in Fig. ) in the perfectly face-on (cos(θ ) = 1) and side-on (cos(θ ) = 0) orientations, respectively. The orientational probability distribution P(cos(θ )) versus cos(θ ) was approximated as a normalized histogram of observations of the value of cos(θ ) for fluid particles found in the interfacial region during the simulation, using evenly spaced histogram bins of width ∆ cos(θ ) = 0.04 between cos(θ ) = 0 and cos(θ ) = 1. P S and P F were taken as the histogram values of the first (probability of 0 ≤ cos(θ ) ≤ ∆ cos(θ )) and last (probability of 1 -∆ cos(θ ) < cos(θ ) ≤ 1) histogram bins, respectively. It was verified that the histogram bin size was sufficiently small and the number of histogram counts sufficiently large that further decreasing it had little effect on the calculated entropy difference.