Next, we analyze features of the electronic structures calculated with the PBE functional. It is well-known that semilocal DFT functionals such as GGA-PBE tend to severely underestimate the band gap of materials while predictions with hybrid functionals (e.g., HSE06) are generally more reliable for semiconductors and insulators. 110-112 However, the large computational cost associated with hybrid functionals makes them unsuitable for high-throughput calculations. Within the dataset of 650 Zintl phases, we focus on compounds that have zero or negative band gap in GGA-PBE calculations and try to identify potentially narrow-gap semiconductors and semimetals. We chose to focus on this subset of Zintl phases to demonstrate the usefulness of the descriptors in materials where bipolar conduction cannot be ignored. The specific procedure we have adopted to identify these narrow-gap semiconductors and semimetals is not important because the material descriptors are generally applicable irrespective of the band gap.