Examples considered in Section 3.3.1 exploit XSAPT's energy decomposition but don't require its reduced scaling. A larger example along the same lines is benzene atop a C 94 H 24 graphene nanoflake, for which XSAPT + MBD results are shown in Fig. . Here, eclipsed-cofacial stacking (analogous to the sandwich structure of benzene dimer) represents a saddle point between symmetry-equivalent slip-stacked minima, where an offset of approximately 1.4 Å lowers the energy by about 1 kcal/mol. The vdW explanation for offset stacking persists in more exotic systems as well. For example, we have examined slip-stacking in models of the covalent organic framework (COF) known as "COF1", 246 models for which are illustrated in Fig. . COFs are layered materials with potential applications in catalysis, but those applications require that the pore structure be open. Although the structures are likely amorphous or polycrystalline, characterized by microdomains, there has been much discussion regarding whether solvent molecules can occlude the pores, 247-249 or whether even the solvent-free structure might be characterized by slippage between the layers that could block the pores. Using the nomenclature of graphene, 252,253 the question is whether these materials exhibit "AA stacking" (perfectly cofacial, with pores open) or "AB stacking" (with alternating offset layers that will occlude the pores). These possibilities are illustrated in Fig. (a) and can be investigated with XSAPT + MBD. Lowscaling methods are crucial because the smallest monomer unit of COF1 is a nine-member ring composed of six-membered rings, containing 102 atoms. The XSAPT + MBD/def2-ma-TZVP calculations presented in Fig. , for the dimer of that fundamental unit, are updates from previous calculations using def2-SVPD, 199 taking advantage of improved memory management in the new code to improve the basis-set quality. These energy profiles indicate a small lateral offset of These possibilities are illustrated in Fig. and can be investigated with XSAPT + MBD, whose low cost is crucial because the smallest monomer unit of COF1 is a nine-member ring composed of six-membered rings, containing 102 atoms. Energy component profiles for the dimer of that fundamental unit are shown in Fig. . The minimum exhibits a small lateral offset of 1.5 Å, much smaller than the pore size, which is more consistent with benzene dimer and other small π-stacked systems than it is with true AB-stacking. As seen in Fig. , the slight offset in the (COF1) 2 model originates mostly from E vdW , although E elst makes a nontrivial contribution to the well depth.