These include bbr, c2c2pd, c3a, c3gc, 2a,2b, 4a, 5a, and 6a. In addition to these standard benchmarks, we also consider dimers of polybenzenoids from the circumcoronene sequence, including coronene dimer [(C 24 H 12 ) 2 ], circumcoronene dimer [(C 54 H 18 ) 2 ], and circumcircumcoronene dimer [(C 96 H 24 ) 2 ]. These are models of graphene nanoflakes and we place them in a cofacial arrangement ("AA stacking"), 71-73 at 3.8 Å face-to-face separation. (This is the same separation as in the cofacial or "sandwich" isomer of benzene dimer, but slightly larger than the 3.354 Å stacking distance in graphitic carbon, which corresponds to offset or "AB" stacking. ) These graphene models are considered alongside the corresponding models of graphane, namely, perhydrocircumcoronenes that are also shown in Fig. . Some previous benchmarks exist for these model complexes.