3.4. Distance Dependence. Having examined twodimensional potentials for lateral displacements of one arene the (x, y) plane of the other, we next consider how the energy profiles for lateral displacement change with respect to the face-to-face separation, R. Thiophene dimer has one of the larger face-to-face separations in its minimum-energy geometry (R = 3.9 Å), and in Fig. we examine one-dimensional energy profiles at that value of R, but also at a larger and a smaller value. These represent three different regimes for the electrostatics. At R = 4.3 Å (Fig. ), E elst is repulsive across the entire range of lateral displacements whereas E elst is strictly attractive for R = 3.4 Å (Fig. ). At the intermediate value R = 3.9 Å, E elst ≈ 0 across the whole range of lateral displacements (Fig. ). We consider these three cases in turn.