From the final NPT run, we take a snapshot of the homogeneous single-crystal, cut out the primitive unit cell, and optimize it with DFT at the PBE+MBD level of theory (bottom row of Table ). The DFT optimization at 0 K mainly leads to a shortening of the a-axis by 8% corresponding to a tighter stacking of neighboring polymer backbones. This is also evident in the increased mass density (1.51 g/cm 3 for the DFT compared to 1.48 g/cm 3 for the MD run). We also notice that in the DFT structure, all angles are very close to 90 • (less than 1% deviation), suggesting an orthorhombic crystal. As already seen in the NPT run, in the crystal structure, the stacked chains now adopt a planar backbone conformation in contrast to the non-planar isolated chains (Fig. ). In panel b), we see that the thiophene rings of neighboring chains (along the short stacking axis in a-direction) are not aligned on top of each other, but instead, they are shifted along the backbone direction (b direction in Fig. ) by one thiophene-thiophene distance. This creates space for the benzenethiol groups making the side chains from adjacent layers staggered and thus sterically less contentious.