Two primary data sets were analyzed in this benchmark. The first set is a randomly chosen subset of approximately 8,400 species from PubChemQC's approximately 3.2 million known small (molecular weights less than 500 a.u.) organic molecules. It was chosen to provide a strong basis of comparison as a set of molecules for which we expected GFN2/D4 to perform well. The second "wide [polarizability] range" set is drawn from previous studies and designed to cover a very wide range of polarizabilities. Drawing from the pool of hexamer structures we had created with our GA, we constructed a set of 54 hexamers with GFN2/D4 predicted polarizability values in the approximate range of 80-280 Å3 . In order to balance out our benchmark set, we also added 19 conjugated oligomers and small molecules with GFN2/D4 predicted polarizability values in the "medium polarizability" range of 4-91 Å3 . Hexamer equilibrium geometries were found using preliminary force-field optimization using OpenBabel 18 with MMFF94 or UFF followed by geometry optimization using GFN2. Equilibrium geometries for the medium polarizability molecules were optimized with ORCA 4.0.0.2 using DFT with the B3LYP functional and 6-31G(d) basis set. All polarizabilities reported in this study are isotropic, meaning they are the average of the diagonal elements of the polarizability tensor. We chose to focus on static, isotropic polarizabilities for this study due to their general applicability to a variety of theoretical and computational fields, including method development, dispersion correction, and polarizable electrostatics. For GFN2 calculations, polarizabilities were calculated using xTB which relies on the D4 method in which polarizabilities are calculated using a weighted sum of precomputed atomic polarizabilities. DFT calculations were performed in Gaussian 09 for the PubChemQC set and ORCA 4.0.0.2 26 for the wide range set, both analytical derivatives and coupled-perturbed equations.