Continuum-solvation methods solution acidity

To illustrate this approach, let us consider a recent paper by Toth et al. [117]. The authors used CBS methods (Petersson et al. [21]) and the G2 family of methods to compute gas-phase energy differences between six different carboxylic acids and their respective anions. Two different continuum solvation methods, SM5.42R (Li et al. [139]) and CPCM (Barone and Cossi [118]) were used to calculate the differences in solvation free energies for the acids and their anions. By using this data, relative pK values were determined for each acid using one of the acids as reference. They found that the pKa value of an unknown from a known molecule can be predicted with an average error of 0.4 pK units. It must be noted, however, that this level of accuracy was reached using different levels of theory to describe the processes occurring in the gas phase and in solution. 

---