The three subsets were combined to form the full data set used to initiate AL, which was performed in four phases. In the first phase, the ACE potential was trained on the full data set and used in AL with MLP-MD initiated from Mg 2+ -water cluster (structure selected from a subset (ii)). During the MLP-MD dynamics step, the cluster was constrained in its spherical shape by a flat-bottom spherical bias potential set at a distance of 8 Å from the Mg 2+ cation, applying a harmonic restraint of 500 kcal/mol Å-2 . MD simulations during AL were performed in an NVT ensemble at 400 K. New structures were selected using the similarity selector with a threshold of 0.999, with maximum time in AL set to 7 ps. This longer AL time compared to the gas phase complex was used to account for the higher flexibility of water molecules outside the first solvation shell. The first phase collected 11 structures, which were added to the data set.