We compared the computed electric field gradient (EFG) tensor against experimentally reported values for C Q and η Q . (the algebraic definitions can be found in Supporting Information, Section V). The diagonalized EFG tensor for quadrupolar nuclei also can be translated into these convenient algebraic expressions, C Q and η Q , that reflect the appearance of the experimentallymeasured spectra. For quadrupolar species such as Al, both C Q and η Q values from the EFG tensor are often compiled in the literature. Figure shows the correlation between experimentally measured C Q and the corresponding values calculated by DFT packages (VASP and CASTEP). It is not possible to measure the sign of C Q using 1D NMR spectrum, a special double resonance experiment must be used in this case , thus nearly all experimental papers choose to report the magnitude of C Q . Thus, in figure thie point, we also directly compared the DFT and experiment EFG principal components (V XX , V YY , V ZZ ) in Supplementary Information section X. We note two outliers using the same confidence interval sampling method used previously. Two significantly different C Q values of β-AlF 3 were reported by previous publications with one stating the C Q of the single Al site in β-AlF 3 is 3.4MHz while the other one stating a C Q of 0.8 MHz. Our calculation result (-1.31MHz) suggests that 0.8MHz appears closer to the computed value, and this result is supported by a more recent publication in 2014. The second outlier is the previously noted (CaO) The correlation between experimentally-reported η Q and DFT-computed values for η Q is shown in figure . Any correlation between computed and experimental values is tenuous, at best, with many outliers. It is unsurprising because asymmetry parameters are often difficult to accurately extract from an experimental spectrum for shielding and EFG tensors . Some experimentalists resort to assuming an η Q value based on knowledge of the crystal structures, usually as 0 or 1. On the other hand, both CASTEP and VASP show a strong correlation, R 2 =0.95, which suggests that these codes remain self-consistent with respect to the full EFG tensor. Consequently, we are demonstrating that the experimentally-reported asymmetry parameter may not be sufficiently robust for benchmarking comparisons.