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Hydrophobic solvation of methane and nonbond parameters of the TIP3P water model

In the process of studying the solvation of simple hydrocarbons, we found that the nonbond van der Waals (vdw) parameters for the TIP3P water model could be adjusted without significantly changing its liquid water properties. By increasing the van der Waals well depth ϵ from 0.152 kcal/mol for the TIP3P model to 0.190 kcal/mol (model TIP3P_MOD), the solvation free energy of all‐atom methane changed from 2.5 kcal/mol to 2.1 kcal/mol, much closer to the experimental value of 2.0 kcal/mol. This change of van der Waals parameters does not change hydrophilic solvation, since calculations using either water model lead to the same relative solvation free energy between ethane and methanol. The solvation free‐energy differences between methane and ethane and between ethane and propane have also been calculated with both models, and results found with the two water models are similar. For the united‐atom hydrocarbon model, however, the solvation free energy of methane changed from 2.1 kcal/mol with TIP3P to 1.8 kcal/mol with TIP3P_MOD. © 1995 by John Wiley & Sons, Inc.