Figure shows the DFT energies for the 108 structures in the training dataset, together with the corresponding DFTB predictions with the parameters sets A and B. In general, we found a good agreement for both parameter sets, although there are slightly larger differences in the compression curves for the pure element with the parameter set A. This is consistent with the low weight obtained for pure elements in this set (see table ). Therefore, this greater variation in the energy for the pure elements is mainly a consequence of our weight optimization procedure. Here we recall that our priority is to achieve transferability over a wide range of mole fractions by focusing our model on reproducing the - ReaxFF potential for this system, and the differences obtained in the formation energies, in this case, are smaller.