Thermodynamics of cavity formation in water. A molecular dynamics study

Thermodynamic quantities related to the solvation of hydrophobic solutes in water can be approximated by the application of scaled-particle theory. The crucial quantity is the Gibbs free energy of cavity formation. A series of six molecular-dynamics simulations of water including repulsive cavities of various sizes has been carried out. Using perturbation statistical mechanics, the free energy has been derived as a function of cavity radius up to 0.32 nm (0.32 nm approach of water oxygens to the cavity centre). The free energy agrees well with predictions from scaled-particle theory and the experimental surface tension is predicted to within 5%. The radial distribution of water molecules with respect to the cavity has been determined for five cavity sizes; for one size (radius of approach of water oxygens of 0.3 nm) the orientational distribution and the residence-time distribution in the hydration shells has been determined.