Figure (b) illustrates the distribution of the MAE of forces predicted on the same test set by the MACE models trained on 300, 500, and 1,000 structures, respectively. For all training set sizes except 1,000, two distinct peaks are shown in the distribution. The left and right peaks in the low and high MAE regimes highlight the existence of properly sampled and under-sampled regions of the configuration phase space, respectively. For 300 training points, the right-side peak is cen-tered at 0.54 kcal/(mol•Å) for the model with default species and thus has slightly better accuracy for those under-sampled regions than the model with orbits, which shows a broader right-side peak centered at 0.58 kcal/(mol•Å). The difference between the two models is highlighted in well-sampled regions of configurational space. For the left-side peak, the model with orbits has higher accuracy than the default model with a peak centered around 0.23 kcal/(mol•Å) as opposed to 0.30 kcal/(mol•Å). In total, the two models present similar overall accuracies, with the inclusion of orbits favouring the well-sampled regions.