To examine this in detail, we used XSAPT + MBD calculations to examine intermolecular interactions in (C 20 H 10 ) 2 in a sequence of calculations in which we gradually flatten each monomer at fixed intermolecular separation, starting at the equilibrium dimer structure (with concave monomers) and ending at a structure in which both monomers are planar (so µ = 0). 148 Results of the energy decomposition along this coordinate are plotted in Fig. . Monomer densities ρ A (r) and ρ B (r) are also shown, with using an isocontour value (ρ = 0.001 a.u.) that is typical for exhibiting molecular size. These plots demonstrate that the monomer densities do significantly interpenetrate at the equilibrium stacking distance.