We considered "free" tetramers of stacked azobenzenes with intermolecular separation distances of 5.5 Å (Figure ) and 3.5 Å (Figure ), as well as "constrained" tetramers, surrounded by additional azobenzene molecules, reminiscent of SAMs (Figure and, respectively). The lattice parameters are a = 5.50 Å and b = 9.43 Å in Figure , and a = 3.50 Å and b = 6.00 Å in Figure (the a/b ratio is the same in both cases, a/b ≈ 0.583). For the SAM models, we used a quantum mechanics/molecular mechanics (QM/MM) approach, treating the central tetramer with QM and the perimeter molecules with MM.