Here, we consider some additional large-system benchmarks starting with another set of calculations for the L7 complexes, the results of which are shown in Fig. . Data for MP2 and SAPT0(HF) emphasize the failure of second-order perturbation theory for systems involving large, conjugated monomers. In contrast, XSAPT + ai D3 and (especially) XSAPT + MBD perform extremely well for these systems. This is true even in comparison to state-of-the-art semi-empirical methods designed for noncovalent interactions, exemplified in Fig. by the HF-3c 167 and PBEh-3c 168 methods. These methods are designed for geometry optimization of large molecules and they complement XSAPT by providing an affordable means to obtain geometries, for which reliable interaction energies can then be computed using XSAPT-based methods. Figure presents E int benchmarks for a set of large host-guest complexes common to the S12L and S30L data sets. Unlike other benchmarks discussed in this chapter, which come primarily from CCSD(T)/ CBS calculations, these are obtained from experimental association energies (∆G • ), back-corrected to gasphase interaction energies by subtracting theoretical estimates of the vibrational entropy change and the change in solvation energy upon complexation. These benchmarks come with estimated uncertainties of ±3 kcal/mol, with the solvation correction as the largest source of error. MP2-based methods are effectively useless for these systems and even B97M-V, which is usually an outstanding semilocal functional for noncovalent interactions, 171 exhibits a MAE of 6 kcal/mol and a maximum error of 11 kcal/mol. Notably, these are CP-corrected B97M-V/aug-cc-pVTZ calculations that should lie near the CBS. In complexes of this size, BSSE effects can reach 50 kcal/mol or more in double-ζ basis sets. As with the large-monomer L7 complexes, the XSAPT + ai D3 method requires three-body (triatomic) dispersion corrections to achieve reasonable accuracy for this S12L∩S30L data set, whereas those effects are inherent in XSAPT + MBD. The latter method exhibits accuracy comparable to B97M-V(CP)/aug-cc-pVTZ, in a more modest triple-ζ basis set and without the need for CP correction.