The Pnma phases are predicted to have comparable and low κ el , increasing with the conductivity to maximum values of ∼ 0.4 and 0.8 W m -1 K -1 at the largest n = 10 20 cm -3 we tested (Fig. ). On the other hand, the intrinsic p-type conductivity of the R3m systems results in a much larger κ el , of around 3 and 3.5 W m -1 K -1 for R3m GeS and GeSe, respectively, which reduces to 1.6 -2 W m -1 K -1 at large n. This indicates a somewhat complex relationship between the carrier concentration, σ and κ el in the R3m systems, but is again similar to our previous calculations on rocksalt SnS and SnSe. At a fixed n = 2 × 10 19 cm -3 , which is a conservative estimate of the achievable p-type doping levels in SnSe, the PFs of p-doped Pnma GeS and GeSe show a slow decrease, while the S 2 σ of the n-doped phases peak at intermediate temperature and fall at higher T . In both cases, this is a product of a reduction in the σ with temperature and a rise in the S (Fig. ). On the other hand, at this n the S of the two R3m phases are predicted to fall with temperature, leading to a significant drop in the PFs at higher T .