To sample the NVT ensembles, the LangevinMiddleIntegrator integrator, with a friction coefficient of 20 ps -1 , was used. We note that, at 50 o C, both ice polymorphs are metastable with respect to liquid water; however, within the sampling performed to gather data for training PGM models, no melting events were observed. All simulations were performed with a timestep of 2 fs, saving a configuration every 50 time steps.