(color online) Atomic structure of 4 × 4 monolayer SnO from the top view and the side view. The red and dark grey spheres represent Sn and O atoms, respectively. We take i to mark the doped pair, Mn (0, i), in which the first doped atom occupies the fixed Sn position, labeled 0 in the diagram, and the second doped atom takes position i = 1–8.