A Γ-centered k-grid of 1 × 8 × 1 was used for the optimization of the single chain structures, and that of 8 × 8 × 4 for the optimization of the HT-HT crystal unit cell. The band structure of the HT-HT crystal was calculated on a finer k-grid of 32 × 32 × 12. For the bigger HH-TT supercells, a coarse k-grid of 1 × 8 × 1 was used.