FREE-ENERGY OF THE HYDROPHOBIC INTERACTION FROM MOLECULAR-DYNAMICS SIMULATIONS - THE EFFECTS OF SOLUTE AND SOLVENT POLARIZABILITY

Molecular dynamics simulations are used to calculate the free energy o f methane association in water, using the polarizable fluctuating char ge model that treats the charges on atomic sites as dynamical variable s. Compared with previous studies using nonpolarizable potentials, the inclusion of polarizability leads only ro small differences in the me thane pair potential of mean force. This is in contradistinction to tw o previous studies using other polarizable models, which do not agree with the nonpolarizable results or with each other. The potential of m ean force is calculated at three different temperatures (283, 298, and 313 K) from which the temperature dependence and also the entropic pa rt of the free energy is examined. It is found that the tendency for m ethane molecules to aggregate increases with increasing temperature an d that aggregation is stablized by entropy.