The original SMD parameterization was done with the Gauss-Bonet tessellation scheme, while the default tessellation scheme in GAMESS is FIXPVA . While this di erence in tessellation scheme has a negligible e ect on the solvation free energies of neutral molecules, it can have a rather larger e ect for ions. Thus, for calculations involving the original SMD radii we use the Gauss-Bonet tessellation scheme (mthall=1 in the $tescav input group), while we use the more numerically stable FIXPVA scheme when optimizing the radii. The original SMD parameterization was also done with integralequation-formalism PCM (IEF-PCM) while we chose the C-PCM method as it is computationally significantly more e cient for semiempirical calculations. COSMO is used with AM1, PM3 and PM6 as implemented in the MOPAC program . The null model is constructed by setting all the predicted solvation free energies to the average of all the reference energies and the error bars reflect 95% confidence limits .