  We used density functional and many-body perturbation theory to calculate the
quasiparticle band structures and electronic transport parameters of p-type
SnSe both for the low-temperature Pnma and high-temperature Cmcm phases. The
Pnma phase has an indirect band gap of 0.829 eV while the Cmcm has a direct
band gap of 0.464 eV. Both phases exhibit multiple local band extrema within an
energy range comparable to the thermal energy of carriers from the global
extrema. We calculated the electronic transport coefficients for single-crystal
and polycrystalline materials to understand previous experimental measurements.
We also discuss the dependence of the transport coefficients on doping
concentration and temperature to identify doping conditions for optimal
thermoelectric performance.
