An initial GAP model is fitted using the optimized hyperparameters for the AL4GAP-generated configurations across multiple-compositions (Fig. ), with "labels" computed using DFT-SCAN calculations. To circumvent the limitations of Boltzmann sampling, we showed in Guo et al. that metadynamics can be used to sample out-of-equilibrium training regions by utilizing the initial GAP model for LiCl-KCl as a model system . Here we briefly reproduce the details in utilizing the well-tempered variation of Metadynamics sampling on the newly AL4GAP generated GAP model for an equal fraction of molten salt mixture (e.g., 50% molar fractions of LiCl and KCl) to perform configurational sampling near the melting point as a reference temperature, which potentially leads to improved coverage of the training space . The unlike atom-atom ion pair (e.g., Li-Cl, K-Cl) coordination has been chosen intuitively as a collective variable (CV) to drive the exploration. The atom-atom pair coordination CV is parametrized with the values of the first minima in the partial PDFs. A Gaussian was deposited every 250 fs with a bias factor equal to 50. The potential is subject to retraining with an actively learned configuration drawn from this metadynamics sampling. A more detailed discussion is available in Guo et al.