where the "KS" superscripts indicate that these terms are evaluated using DFT orbitals and energy levels. This represents a potential mismatch between the KS response terms in Eq. ( ) and their HF analogues that are subtracted in Eq. (10). We leave it to benchmark calculations to determine the extent to which this is a significant problem. Whatever the form of the monomer SCF wavefunctions, SAPT0 or SAPT0(KS) is MP2-like in its treat- ment of dispersion. This lends some drawbacks because MP2 itself is not a benchmark-quality method for noncovalent interactions because dispersion energies can be significantly overestimated, especially in large molecules. MP2 includes no correlation in the dispersion energy, 73 but it is questionable whether any finite-order MPn method is appropriate to describe dispersion in systems whose monomers are large and polarizable, 72 e.g., due to extended conjugation. Exaggeration of dispersion interactions is exacerbated as the CBS limit is approached, as demonstrated in Fig. using HF-based SAPT0 applied to the S66 data set. This is a standard database of 66 small dimers, containing ≤ 10 second-row atoms, for which CCSD(T)/CBS benchmarks are available for comparison.