Fig. 2.

Calculations of the PMF. (a) Mean effective force between two methanes in water as a function of their separation. When the methane–methane separation is <3.6 Å, the repulsive force between two methane molecules in vacuum is used. For methane–methane separations >6.0 Å, we use a larger unit cell containing 139 water molecules, instead of 63. A constant force derived from the surface-tension model (5) is also shown. (b) The PMEF (with volume-entropy term), the PMF (without volume-entropy term), and the potential of surface tension between two methane molecules as functions of methane–methane separation.