Throughout the rest of this paper, we will apply periodic boundary conditions (PBC) along the axis of the polymer backbone. As a further simplification, we only consider regioregular (RR)-conjugated polymer chains, which follow a strict orientation of the alternating asymmetric repeating TBT units throughout the polymer backbone. This is, of course, an idealization of the real system in which the degree of regioregularity depends on synthetic conditions. Given the three possible connections between two TBT units (HH, HT, TT), there are two feasible RR-chains, namely HH-TT and HT-HT (cf. Fig. ). We compare the structural properties of these regioregularities obtained from MD and DFT (cf. Table ). Our results show that the presence of the benzenethiol groups leads to a deviation of the backbone planarity compared to the unsubstituted planar polythiophene chain. Such distortions from planarity have been observed for polythiophene systems substituted with similar bulky aromatic groups and can be related to steric effects between the side groups. For the HH-TT regularity, this is more prominent than for the HT-HT regularity because of the proximity of the benzenethiol groups in the HH intermonomer junction (cf. Fig. , Table , and Supporting Text).