For double-ζ basis sets, the use of a supramolecular basis (i.e., CP correction) significantly reduces the importance of diffuse basis functions, and we find for example that CP-corrected def2-SVP and def2-SVPD values of ∆E int are similar, except in the case of doublehybrid functionals, whereas in the absence of CP correction the diffuse functions significantly alter ∆E int . For the coronene dimer, we find that double-ζ basis sets predict an incorrect intermolecular separation unless CP correction is applied, whereas the CP-corrected double-ζ geometry agrees with results obtained using quadruple-ζ basis sets. These are important observations, given that diffuse functions are expensive and numerically problematic for large systems.