For the case of FAU, the first set of preliminary FF-based simulations delivered configurations having both CBZ molecules in the same cage as lowest-energy cases. DFT calculations for five of these configurations resulted in a Boltzmann-weighted adsorption energy of -137 kJ mol -1 , an increase by about 16 kJ mol -1 with respect to the 1CBZ@FAU case. In the lowest-energy configuration, shown in the top panel of CBZ polymorphs, the formation of π-π stacked dimers with so many short contacts between the rings does not appear to occur, presumably because these dimers could not be packed efficiently into a crystal structure. In other words, the stabilization of this bonding motif is directly related to the confinement to the FAU supercage. In contrast, hydrogen-bonded anti dimers, very common in CBZ polymorphs, could not form within a single supercage due to steric restrictions. They could, however, be accommodated in two adjacent supercages, with the hydrogen bonds pointing through the connecting 12MR window. To investigate this possibility, FF-based simulations were carried out for FAU models having two CBZ molecules in adjacent cages. Among the five configurations that were optimized using DFT, the lowest energy was found for the only configuration where the CBZ molecules interact through a pair of -N-H•••O hydrogen bonds (bottom panel of Figure ). Even though stabilizing guest-guest interactions are even larger for this system when compared to the π-π stacked dimer in a single supercage, the adsorption energy is slightly less negative (Table )