Part of the impetus for this work were the relatively large error in pKa values predicted using PM3/COSMO compared to PM3/SMD with the original SMD radii observed by Jensen et al. , so we use the new SMD radii to compute the pKa value using the same data set. The data is presented in Figure and Table and shows that the RMSE drops from 1.5±0.3 to 0.9±0.3 pH units for PM3/SMD † and 2.0±0.4 to 1.6±0.3/0.4 pH units for DFTB/SMD †. In both cases the improvement is primarily a result of the decrease in mean error (ME), i.e the original radii led to a fairly systematic underestimation of the pKa values that has now been removed by the reparameterization. For DFTB the increased accuracy is also due to a larger number of low error predictions as is evident in Figure . In the case of PM3/SMD † the accuracy is now very similar to PM3/COSMO. The RMSE for PM6/SMD † is similar to PM6/COSMO and larger than for PM3/SMD in analogy with the corresponding results for COSMO.