The final set of DFT computed 7 Li EFG tensors over structures of Li 3 PS 4 contains 166 diverse structures from the LPS UFP model, which have a total of 14,448 Li environments. The EFG tensor for each atom is calculated for all the structures using the plane-wave pseudopotential DFT code CASTEP v22 . The hyperparameters for the SA-GPR descriptor are optimized as described in the Supporting Information, using a 5-fold cross validation procedure with a test set, which is withheld from training. The resulting mean absolute error (MAE) for the test set in ! Q is 7.4 kHz, and the correlation plot is shown in Figure . It is important to note that the density of points of ! Q within the red bars is high, and thus this representation highlights the outliers as they are clearer to distinguish from the majority.