A New Hybrid Method for the Calculation of the Solvation Free Energy of Small Molecules in Aqueous Solutions.

The ability to accurately predict the solvation free energies of ionic species using the appropriate thermodynamic cycle is of great importance in many areas of chemistry and biochemistry. To improve the accuracy of calculating solvation free energies we devised a hybrid cluster-continuum approach, where explicit solvent molecules are added to the traditionally employed continuum model. Our computational workflow consists of the following steps: First, the minimum number of explicit water molecules beyond which additional water molecules no longer improve the accuracy of the cluster-continuum model is carefully established. The convergence values for fully relaxed molecular configurations are compared with those obtained by sampling thermally disordered configurations using single-point calculations. We find that the dielectric constant does not have a significant influence on the solvation free energy, while accounting for the placement of a counter ion is necessary for the accurate calculation of the solvation free energy.