The last system that we consider is tartaric acid, (2 R, 3 R) -C 4 H 6 O 6 , for which experimental data are available. We used the same geometry and basis set (6-31G(d)) as in Rérat et al., but the calculations were performed with HSE06 rather than PBE0 because the former is computationally more efficient. The k point grid is 6 × 8 × 8. The geometry was also rotated so that the coordinate axes coincide with the principal axes of the symmetric part of the mixed-gauge electric dipoleelectric dipole polarizability, which is the best representation of the coordinate system for the LG(OI) approach as explained in Ref. 3. The unit cell geometry is reported in Table of the SI.