Despite the recommendation against double-ζ basis sets, with CP correction the ωB97M-V interaction energies are remarkably close to def2-TZVPD results, within 3 kcal/mol in all cases except 6-31G*. In fact, M06-2X exhibits slightly larger deviations between CP-corrected double-and triple-ζ results. It is perhaps surprising to note also that diffuse functions have only a small effect when CP correction is used, e.g., 4 kcal/mol difference between def2-SVP and def2-SVPD results, and < 0.5 kcal/mol difference between def2-TZVP and def2-TZVPD. Presumably, the use of a supramolecular basis set facilitates a good description of the tails of the wave function, whereas in the absence of CP correction dif- fuse functions are needed to describe these tails in the monomer calculations. This observation is good news for calculations on systems of this size, where diffuse functions add significantly to the cost and also incur problems with linear dependencies. That said, when double-ζ basis sets are employed, CP correction is essential in order to mitigate the effect of the diffuse functions; without it, def2-SVP and def2-SVPD interaction energies differ by > 20 kcal/mol in some cases. For triple-ζ basis sets, the effect of diffuse functions is 1 kcal/mol even without CP correction.