  Rock-salt structured chalcogenides, such as PbTe, PbSe, and SnTe, are the top
candidates for mid-temperature thermoelectric applications, and their p-type
thermoelectric efficiencies can be enhanced via aligning the valence bands.
Here, we provided comprehensive numerical investigations on the effects of band
convergence on electronic properties. We found that the extra valance band can
indeed significantly enhance the power factor. Nevertheless, the extra valance
band can also increase the electronic thermal conductivity, which partially
offsets the enhanced power factor for the overall figure-of-merit. Finally, we
predicted that the maximum figure-of-merit for PbTe, PbSe, and SnTe can reach
to 2.2, 1.8, and 1.6, re-spectively, without relying on the reduction in
lattice thermal conductivity.
