Initial tests showed that the solvation free energy does not vary greatly with a change in radii for neutral molecules and the flatness of the energy surface caused problems for the Nelder-Mead method. Furthermore, the error for the ions is considerably larger than for the neutral molecules. Thus, only radii of the ions are optimized but when testing the performance of the new radii neutral molecules are included. This means that the optimum parameters obtained for the ions will not necessarily lead to the lowest possible error for neutral molecules. We therefore test the e ect of optimizing a subset of the radii but include all molecules when testing the overall performance. These results are presented in Tables and and in Figure .