(color online) Schematic views of structure for (a) 4×4×1 and (b) 6×6×1 AlN nanosheet supercells. Pink and dark blue spheres represent Al and N atoms, respectively. The substituted positions of X dopants are denoted by red in 4×4×1 nanosheet supercells and 0-4 in 6×6×1 nanosheet supercells, respectively.