The testing data set for Mg 2+ cation in aqueous solution consisted of 51 structures collected over 50 ps NVT dynamics of Mg 2+ solvated in a cluster of 51 water molecules. The spherical shape of the cluster was kept by a harmonic spherical potential placed at 7.5 Å from Mg 2+ . Validation results are depicted in Fig. . MACE demonstrates excellent performance in energies and forces, with MAD of 0.31 meV/atom and 18 meV Å-1 for energies and forces, respectively.