Based on the results in the previous subsection we optimize the Coulomb radii for PM3, PM6, and DFTB independently, while leaving the non-polar solvation free energy contribution unchanged. We use the Nelder-Mead simplex method to optimize the radii using the SMD data set with the SciPy package using a custom optimization script. Optimization of the radii is done by minimizing the RMSE with respect to the radii.