The OR was computed using standard linear response methods as discussed in section 2. Three choices of gauge were considered: modified velocity gauge (MVG), length gauge (LG), as well as the newly developed origininvariant length gauge [LG(OI)]. LG calculations were performed with gauge-including atomic orbitals (GIAOs) for variational methods (B3LYP, CAM-B3LYP ) and without for CCSD. Thus, CCSD-LG OR calculations are inherently origin dependent. The two density functionals were chosen as representative members that provide reasonable OR values. A test set of 50 molecules with a wide range of molecular sizes and OR magnitudes was compiled from previous OR studies, see Figure . Molecular geometries were also obtained from these sources, as detailed in Tables S1-S50 in the Supporting Information (SI). OR values were calculated for the whole set using DFT methods and for the first 17 molecules in Figure using CCSD because of computational limitations.