  Dopants positioned near edges in nanostructured graphene behave differently
from bulk dopants. Most notable, the amount of charge transferred to
delocalized states (i.e. doping efficiency) depends on position as well as edge
chirality. We apply a self-consistent tight-binding model to analyze this
problem focusing on substitutional nitrogen and boron doping. Using a Greens
function technique, very large structures can be studied and artificial
interactions between dopants in periodically repeated simulations cells are
avoided. We find pronounced signatures of edges in the local impurity density
of states. Importantly, the doping efficiency is found to oscillate with
sublattice position, in particular, for dopants near zigzag edges. Finally, to
assess the effect of electron-electron interactions, we compute the self-energy
corrected Greens function.
