POTENTIAL OF MEAN FORCE FOR THE METHANE-METHANE PAIR IN WATER

Molecular dynamics and potential of mean force techniques are used to study methane-methane association in water. The five-site, methane-methane pair potential is taken from recent work by Spellmeyer and Kollman, while the extended simple point charge model is used to model the water-water interactions. The calculated potentials of mean force at 300 and 330 K indicate that the contact wells are significantly deeper than the corresponding solvent-separated wells. The effect of the temperature on the calculated potential of mean force is found to be small. The calculated equilibrium constants suggest that the probability of contact and the solvent-separated pairs are comparable. The shape of our potential of mean force result at room temperature using the extended simple point charge model is very similar to the results of simulations reported by Belie and Wodak using a polarizable water model. It appears that further research is necessary to assess the role of nonadditive effects in modeling of hydrophobic interactions.