Performing Huber regression with a fixed intercept at the origin on the GFN2/D4 and !B97X polarizabilities from our "wide range" set (Figure ), we observed trends similar to those seen in the PubChemQC study. We again observed smaller di↵erences in polarizabilities less than 50 Å3 , with a mean absolute error of 4.72 Å3 (Figure ), and increasingly larger di↵erences as polarizabilities increased, with an MAE of 37.31 Å3 for polarizabilities less than 100 Å3 (Figure ), and an MAE of 145.02 Å3 for the entire set (Figure ). We similarly observed greater variation in polarizability di↵erences as their magnitudes grew, shown by the drastically smaller R 2 value for the full set as compared to the subset with values less than 50 Å3 . Three extreme outliers appeared (Figure ), in which the percent error of the GFN2/D4 calculated value was in excess of 80%. These outliers were run with the same DFT method and basis set using Gaussian (Table ), which confirmed the ORCA results and the presence of troubling random errors in GFN2's polarizability calculations. Examining their chemical structures (Figure ), all notably include sulfur ring systems, suggesting the possibility that this particular motif is not well accounted for by GFN2/D4. Figure : Using the Huber Regressor to perform linear regression robust to outliers (and forcing the y-intercept to 0), GFN2/D4 shows some linear correlation with !B97X cc-pVTZ for isotropic polarizability calculations.