The final comparison is across methods, which can be obtained by using the CBS(TQ) extrapolation with CAM-B3LYP for each gauge as reference for the other methods and basis sets (note that here there is no direct comparison across choices of gauge), see Figure . The results in panel (a) between different functionals indicate that gauge invariance does not lead to the same overall OR values, as the ∆ TQ/CAM-B3LYP U converge to 0.26 at the CBS limit. A reduction in ∆ TQ/CAM-B3LYP U can be seen from the double to triple zeta basis set. However, further increase in basis set size yields little to no improvement. This is due to results from both functionals converging at similar rates and in the same direction to their respective CBS values, such that the difference between OR values remains almost constant as the basis set size is increased. Posi- A comparison with experimental data (used as reference in Eq. 10) is performed for a subset of the molecules: 14, 30, and 41-43, shown in Figure . These compounds were chosen because they are fairly rigid and have a single stable conformer, and experimental data in the gas phase are available. This choice eliminates various difficulties due to solvation effects and averaging over contributions from multiple stable conformers, but it comes at the cost of a limited sample size. Furthermore, contributions from vibrational motions are not included in the calculations. Therefore, these constraints somewhat limit the generality of this comparison. Only DFT methods are used because most of these systems are too large to be treated at CCSD level with large basis sets.