NaZnSb: This is another semimetallic phase that is identified as a promising candidate. Tetragonal NaZnSb (P 4/nmm, no. 129) crystallizes in a layered structure with antifluorite-like (Zn 2 Sb 2 ) 2 layers intercalated with Na (Figure ). NaZnSb belongs to a large family of ternary ABX Zintl phases that adopt many di↵erent structure types. NaZnSb has a calculated band gap of -0.23 eV (more negative than Mg 3 Bi 2 ) and a very high p-type of 45.4, which is attributed to the large valence band valley degeneracy N V,V B = 8 (Figure ). Combined with a low n-type , NaZnSb exhibits a large asymmetry parameter 1/R = 7.2 (R = 0.1). Consequently, we predict that the TE performance of semimetallic NaZnSb is ⇠80% of Mg 3 Bi 2 at 300 K. Gvozdetskyi et al. experimentally studied the TE properties of NaZnSb and found that a maximum zT of 0.23 can be achieved at 675 K. Transport measurements indicate that the material is a degenerate semiconductor with a Goldsmid-Sharp gap of 0.23 eV, which agrees with the calculated band gap of 0.25 eV with modified Becke-Johsnon (mBJ) functional. This is in contrast to the semimetallic electronic structure predicted with GGA-PBE, PBEsol, and HSE06+SOC functionals. It is not clear if Gvozdetskyi et al. included relativistic spin-orbit coupling in their calculations. In fact, if the band gap of NaZnSb is actually +0.23 eV and the other material descriptors ( p and R ) are similar to those computed with HSE+SOC, then we predict the maximum zT 300K to be 2.38⇥ that of Mg 3 Bi 2 . Despite the uncertainty around the band gap, NaZnSb is an interesting candidate worth further theoretical and experimental investigation.