Table : Crystallographic data of the HT-HT single-crystal phase from NPT equilibration simulations at T = 300 K and from DFT optimization of the primitive cell. The first row denotes the block average over the ensemble of the 12 x 12 chains in the ac-plane with the standard deviation due to thermal fluctuations at room temperature in parentheses. The bottom row shows the DFT-optimized (PBE+MBD) results. The results and their respective standard deviations due to temperature and pressure fluctuations are summarized in Table . We see that all angles differ from each other and do not contain the 90 • angle typical for monoclinic crystals. Thus, the HT-HT forms a triclinic crystal structure at room-temperature. The crystal shows only minimal deviations from its equilibrium configuration due to thermal fluctuation (the standard deviation of the aand c-axis is 0.3% and of the b-axis less than 0.1%).