For GFN2/D4 comparison studies with both the PubChemQC and wide range sets, nonaugmented basis sets were chosen with an emphasis on e ciency over absolute accuracy. This was done to estimate how well GFN2 compared generally to DFT, without facing potential resource and/or linear dependence issues likely to arise when using augmented basis sets with large molecules. For the comparison of basis set accuracy, aug-cc-pVTZ was selected as the standard of comparison. This basis set was chosen as the standard because di↵use functions are necessary to describe the long-range electron behavior and electron correlation important for polarizability calculations, demonstrated in by Rowley and coworkers' assessment that augmenting basis sets with di↵use functions leads to a substantial increase in accuracy, particularly for polarizability calculations. This study also determined that aug-cc-pVTZ performed better than both a similar non-augmented triple-zeta basis set and an augmented double-zeta basis set. Additionally, Sauer and co-workers found using larger augmented basis sets do not yield substantial accuracy increases for polarizability calculations despite the increased time required. 11