The comparison of our predictions for the R3m phases to experiments is rather more mixed. We predict a comparable ZT = 0.83 for GeSe at 540 K (n = 8 × 10 19 cm -3 ) to the ZT = 0.9 at 500 K predicted in Ref. . On the other hand, the study in Ref. predicted ZT > 2 at 800 K and n ≈ 10 19 cm -3 , whereas we predict ZT < 1 at 800 K at a larger n = 8 × 10 19 cm -3 due to our higher predicted κ latt . Compared to the measurements on GeSe/AgBiSe 2 alloys in Refs 46 and 49 , our calculations predict that much larger n are required to obtain comparable ZT . This can be attributed in part to the high thermal conductivity predicted in these calculations, but we also find that we require a 4× larger n to reproduce the measured σ , which suggests the alloying may also impact the electrical properties. We note, however, that our calculations do reproduce the ZT = 0.84 at 720 K obtained for in (GeSe) 0.85 (AgSbSe 2 ) 0.15 with a reasonable n = 4 × 10 19 cm -3 . We therefore suggest that further characterisation of the R3m phases, to measure the properties of pure phases and to better understand the impact of alloying on the transport properties, is warranted.