To validate our MLFF, we compared per-configuration energies and forces, plus Li + Mean-Squared Displacements (MSD), and harmonic phonons, calculated using our MLFF versus DFT calculations (Figure ). To generate a new dataset of structures distinct from the training dataset, we used AIMD simulations performed at 300 K, 400 K, 500 K, 600 K, 678 K and 800 K from our previous work on Li 3 N . At each temperature, we performed 10 independent AIMD simulations using different random seeds. Each simulation was run for 8000 steps, giving a total of 160 ps independent trajectory data at each temperature. To obtain energies and forces, we randomly selected 20 structures per independent trajectory for each temperature, giving a total of 1200 random structures. We then performed single-point calculations on each of these structure using DFT and MLFF, and calculated the Root Mean Squared Errors (RMSE), Mean Absolute Errors (MAE), and MAXimum absolute errors (MAX) between the DFT and MLFF data. As expected, the errors in energies are larger at higher temperatures due to the complex local environments observed when diffusion occurs at such temperatures..