For (thiophene) 2 at R = 3.9 Å, representing the face-to-face separation in the parallel-displaced geometry, both |E elst | and |E ind | are smaller than 0.2 kcal/mol. This means that E vdW is nearly a quantitative match for E int ; see Fig. . It has previously been claimed that electrostatic interactions control the orientation dependence of (thiophene) 2 , 186 but this statement is inconsistent with the repulsive (but negligible) electrostatic profile. Charge penetration effects, leading to breakdown of the multipole approximation, are clearly more significant than the dipole-dipole interactions in this system. The presence of heteroatoms does not change the qualitative picture relative to benzene dimer.