MOLECULAR-DYNAMICS STUDY OF METHANE HYDRATION AND METHANE ASSOCIATION IN A POLARIZABLE WATER PHASE

Molecular dynamics simulations are used to investigate the influence of adding an explicit polarization term to the water potential on the structural and dynamic properties of aqueous methane solutions and on methane-methane association in water. Calculations are performed using respectively two different water models: the three-center polarizable water model (PSPC), where the many-body effects are treated explicitly using the extended Lagrangian method, and the mean-field classical SPC model. Comparing the results obtained from the two sets of calculations we find that electronic polarization of the water molecules has a subtle though significant influence on the structure and dynamics of water molecules surrounding the hydrophobic solute. But its most remarkable influence by far is on the methane-methane potential of mean force: addition of the polarization term to the water potential effectively abolishes the much questioned solvent-separated minimum found in many previous studies with nonpolarizable water models. Polarizable water models thus appear to yield an improved physical picture of the system and should be well suited for investigating the process of hydrophobic association.