For these 44 Zintl phases, we then estimate a maximum zT at 300 K using the two-band model (Eq. 13). Three independent material descriptors are necessary to estimate zT : band gap (E g ), nor p-type quality factor ( n or p ), and asymmetry parameter (R ). Due to the unsystematic underestimation of the band gap in GGA-PBE calculations, we fix E g to +0.3 eV for all 44 phases. Since larger E g leads to higher zT (Figure ), fixing E g to +0.3 eV allows us to compare the best-case-scenario zT across materials. We perform a scissor operation to adjust E g with the assumption that the band topology remains unchanged. The band e↵ective mass m ⇤ b is an important parameter in the calculation of p and n , and therefore, R . We use a finite-di↵erence method to calculate m ⇤ b from the electronic structure calculated on a dense k-point grid. We also calculate the density-of-states e↵ective mass m ⇤ DOS from m ⇤ b using the relation m ⇤ DOS = N 2/3