Finally, whatever the effort in order to match GTOs with PW results, via CP correction, basis set augmentation or extrapolation, one notices that the best MP2 errors do not reach MAEs lower than 0.05 kcal/mol with maximum differences of at least 0.15 kcal/mol (Tables II, III and IV). While this might at first be taken as an indication that interaction energies are essentially converged at the aug-cc-pV5Z/CP level within an 0.05 kcal/mol numerical accuracy, further analysis instead reveals that residual discrepancies occur because GTO results tend to further deviate from PWs as the system size increases. Figure shows indeed that GTO interaction energies that are not corrected for the BSSE are lower than those from PWs, and that the BSSE tends to become larger with an increasing number of electrons in the system. Interestingly, assuming that the CP correction removes the majority of the BSSE, only the BSIE remains and in turn increases with the system size. Hence, although the size of a GTO basis grows with the number of atoms, the incomplete coverage (lack of completeness) of this expansion leads to a smaller and smaller correction of the BSIE with increasing system size. In other words, for a given GTO basis set, its capacity to capture the (correlation) energy decreases as the size of the system increases. Such a size inconsistency is even more pronounced for the smaller cc-pVXZ bases (Fig. ). In the limit of large bases and systems, however, the occurrence of linear dependencies can further interfere with this behavior.