Fig. represents a correlation plot that compares the performance of the final optimized NN on the SC training set. The AL-NN predictions of energies and the forces for the clusters in the training pool are compared with the reference SC EAM model predictions. We find that the MAE during training is « 20 meV/atom for all the systems and those during testing are also « 20 meV/atom for most elements except Ir and Rh, which have marginally higher error owing to increasing configurational diversity in the far-from-equilibrium region. The predicted MAE in forces are much lower than 0.5 eV/Å for all elements. We also further test the NN using a validation set of 35000 structures never used in the training process. Fig. (b) and (d) show the correlation between AL-NN predicted energies and forces, respectively vs. reference SC EAM model. As expected, we find that the final optimized NN is able to reliably predict the cluster energies for an elaborate test data set generated not only near equilibrium, but also in the highly non-equilibrium region that extends far beyond. As a more rigorous test of the performance of AL-NN, we compute the forces on the atoms for the various clusters in the validation set and compare those with that obtained from SC EAM. It should be noted that the forces were not included as part of the training during the AL iterations. Fig. 4 (d) shows the correlation between the AL-NN predicted vs. SC EAM forces. Each point in this correlation plot represents one of the force components -F x , F y and F z acting on a particle. We find the overall MAE between AL-NL vs SC EAM predicted forces is relatively small i.e MAE « 1 eV/Åfor most elements with Ir and Rh displaying somewhat higher errors (consistent with the trend in the MAE for energies). Given that the NN had not been trained on the forces, this agreement is of excellent quality.