For the Materials Project in particular, potential piezoelectric materials in the database are identified by i) allowing only structures with space groups 1, 3-9, 16-46, 75-82, 89-122, 143-146, 149-161, 168-174, 177-190, 195-199, 207-220 (since these space groups lack inversion symmetry), and in addition ii) the calculated DFT bandgap of the material > 0.1 eV. Compounds in the Materials Project database that satisfy these criteria are selected for a full-DFT calculation of the piezoelectric tensor and derived properties (see below).