The cluster-continuum model for the calculation of the solvation free energy of ionic species

A hybrid approach using a combination of explicit solvent molecules and the isodensity polarizable continuum model (IPCM) method is proposed for the calculation of the solvation thermodynamic properties of ions. This model, denominated cluster-continuum, has been applied to the calculation of the solvation free energy of 14 univalent ions, mainly organic species, and compared with the results obtained with the IPCM, polarizable continuum solvation model (PCM), and SM5.42R continuum methods. The average error in our calculated solvation free energies with respect to experimental data is 8.7 kcal mol(-1). However, the great merit of our model resides in the homogeneous treatment for different ions, resulting in a standard deviation of only 2.9 kcal mol(-1) for the average error. Our results suggest that the cluster-continuum model must be superior to the IPCM, PCM, and SM5.42R methods for studying chemical reactions in the liquid phase, because these continuum methods present a standard deviation of similar to8 kcal mol(-1) for the average error for the species studied in this work. The model can also be used to calculate the solvation entropy of ions. Predicted solvation entropies for five ionic species are in good agreement with available experimental data.