- The calculated values of ∆ QZ are plotted in Figure . These results show that, for the molecular case, both functionals are close to basis set completeness and gauge invariance. However, the differences between aTZ and aQZ for any choice of gauge are considerably smaller than with QZ. For instance, the aTZ-aQZ difference within the same gauge is 2-3% and < 10% between choices of gauge; on the other hand, the difference with either basis set and QZ is 15-25% within the same gauge, and the MVG-LG(OI) difference for QZ is 16-21%. This indicates that the use of diffuse functions is more important than increasing the basis set size from Tζ to Qζ. However, the situation is very different for the PBC calculations. Figure shows that QZ results are 2-2.5 times smaller than the aTZ ones, and 3-4 times smaller than the aQZ ones. The ∆ QZ values are smaller for HSE06/aTZ than for SVWN5, but the opposite trend manifests for aQZ. The difference between choices of gauge is most significant for the aTZ basis set. The change in trend with respect to the molecular case is likely due to the spatial extension of diffuse functions, which may lead to strong interactions between repeated units in adjacent cells.