A recent survey of protein crystal structures confirms this viewpoint. . In either case, the electrostatic potential is approximated using monomer dipole and quadrupole moments computed at a level of theory that is consistent with XSAPT + MBD electrostatics. The corresponding exact results, using full charge densities, can be found in Fig. ) and Fig. neighboring phenylalanines by but demonstrating that the "vdW picture" of π-stacking (driven by E vdW ) better explains the prevalence of parallel-displaced cofacial stacking. As we speculated earlier, 198 the vdW picture provides a much more satisfactory explanation for why offset stacking is so pervasive in protein crystal structures, across disparate electrostatic environments. The reason is that E vdW consists of only short-range intermolecular forces, which are omnipresent for arene-arene interactions regardless of the electrostatic environment. In contrast, it is more difficult to rationalize how an explanation based on longer-range electrostatic interactions could persist across the myriad electrostatic environments that are encountered within different proteins.