The benzene dimer has long been studied by quantum chemists as an example of a π-π stacking interaction, although its archetypal status in that regard has been questioned, because complexes of larger polycyclic aromatic hydrocarbons, starting already with naphthalene dimer, demonstrate a much stronger preference for cofacial stacking as compared to the "T-shaped" or C-H• • • π geometry that is similar in energy in the case of (benzene) 2 but much less stable for larger acene dimers. All of the acene dimers exhibit offset π-stacking, in which the center-to-center coordinate of the aromatic rings is parallel-displaced, e.g., by 1.8 Å in the case of benzene dimer. Although long attributed to a competition between dispersion interactions and quadrupolar electrostatics, the origin slip-stacked π-π geometries (in benzene dimer, larger acene dimers, and in benzene on the surface of graphene) has more recently been shown to arise from a competition between dispersion and Pauli repulsion, with electrostatics playing a negligible role in driving offset stacking. (In larger acene dimers, electrostatics does play an important role in stabilizing cofacial geometries relative to T-shaped orientations. )