Examining the E int surface for (COF1) 2 (mesitylene) in Fig. , we note that the global minimum (with E int = -128 kcal/mol) resides not at the coordinate origin but rather at x = -1.25 Å and y = 0. Two other minima with nearly identical interaction energies can be found at x = 0 and y = ±1.25 Å. For displacements 2 Å along either x or y, however, the total interaction quickly becomes repulsive as one of the COF1 monomers encounters the intercalant. This behavior is modeled rather well by the vdW potential (Fig. ), which exhibits three minima in roughly the same locations as those in the E int surface. None of the other energy components show this type of behavior. The electrostatic interaction, in particular, exhibits a local maximum at the coordinate origin and becomes increasingly attractive upon lateral displacements, including displacements greater than 2 Å, while the exchange interaction is repulsive everywhere in this example. The dispersion energy is most attractive at the coordinate origin, in contrast to results in Ref. 18 that were discussed above. Unsurprisingly, steric interactions prevent further slip-stacking in this system. This analysis suggests that the structure is more likely to exhibit "AA" stacking (albeit possibly with an offset) when the pores are occupied by solvent, but that staggered ("AB") configurations might occur when the pores are empty, especially in an amorphous or polycrystalline material where individual micro-domains may be kinetically trapped in geometries other than the free energy minimum, because the solvent-free material exhibits broad swaths of configuration space where the potential is strongly attractive. In any case, the vdW potential retains its interpretive power even in the presence of a mesitylene guest. 3.3. Additional COF-1 Models. Our calculations for (COF1) 2 agree with previous theoretical studies that predict offsets of 1.4-2.8 Å that have been computed for this and other COFs, including COF-1. Those studies were performed either using supramolecular DFT or sometimes with force fields, in the interest of using relatively large model systems. (The COF-1 monomer unit in Fig. already contains 102 atoms.)