Along with the structural dimensionality, it is useful to extract quantitative values of the effective masses of the ternary PS semiconductors for which a band structure calculation is available on MP. The direction-averaged effective masses of holes and electrons (extrapolated using the BoltzTrap2 package ) in these PSs are displayed in Fig. . We find that a few compounds have low effective masses in both the valence and conduction band. Some examples are the previously identified Ag 3 PS 4 (mp-12459), Cu 3 PS 4 (mp-3934) and Na 3 PS 4 (mp-28782), the newly identified Zr(PS 3 ) 2 (mp-8203) , as well as various narrow-gap compounds with d-and f-block metals.