The lattice parameters are in good agreement with available measurements, suggesting that PBEsol+D3 provides a good description of the structures. With the exception of P42/nmc Bi2Se3 and R3 ̅ m* Bi2Te3, the calculated and experimental values are within 4 %. For these two structures, a larger deviation of ~10% is observed, which can be explained by the fact that these phases are prepared under high-pressure and high-temperature (i.e. non-ambient) synthesis conditions. For Bi2S3, the calculations predict the Pnma phase to be more stable than the R3 ̅ m phase by 2.9 kJ mol -1 atom -1 . For Bi2Se3, the stability is reversed, with the R3 ̅ m being more stable than the Pnma phase by 1.8 kJ mol -1 atom -1 . The P42/nmc phase is predicted to be much higher in energy than either of these, which we again ascribe to it being prepared under non-ambient conditions. The calculations again predict the R3 ̅ m phase of Bi2Te3 to be more stable than the Pnma phase, this time by a larger energy difference of 5.6 kJ mol -1 atom -1 . This is small enough that the Pnma phase may be accessible, but there are no experimental reports of its synthesis. As for the non-ambient P42/nmc phase of Bi2Se3, the R3 ̅ m* phase of Bi2Te3 is predicted to be considerably higher in energy than both the R3 ̅ m and Pnma phases. This can be understood by the different atomic ordering in the quintuple layers: in the R3 ̅ m phase, layers of Bi 3+ are sandwiched by oppositelycharged layers of Te 2-layers, which is electrostatically favorable, whereas the R3 ̅ m* phase has adjacent layers of Te atoms that depending on the electron density distribution may result in less favorable electrostatic interactions and/or some level of electrostatic repulsion.