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-met hane pair potential is taken from recent work by Spellmeyer and Kollma n, while the extended simple point charge model is used to model the w ater-water interactions. The calculated potentials of mean force at 30 0 and 330 K indicate that the contact wells are significantly deeper t han the corresponding solvent-separated wells. The effect of the tempe rature 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 o ur potential of mean force result at room temperature using the extend ed simple point charge model is very similar to the results of simulat ions reported by Belie and Wodak using a polarizable water model. It a ppears that further research is necessary to assess the role of nonadd itive effects in modeling of hydrophobic interactions.