  To understand the interaction between nitrogen dopants and native point
defects in graphene, we have studied the energetic stability of N-doped
graphene with vacancies and Stone-Wales (SW) defect by performing the density
functional theory calculations. Our results show that N substitution
energetically prefers to occur at the carbon atoms near the defects, especially
for those sites with larger bond shortening, indicating that the defect-induced
strain plays an important role in the stability of N dopants in defective
graphene. In the presence of monovacancy, the most stable position for N dopant
is the pyridinelike configuration, while for other point defects studied (SW
defect and divacancies) N prefers a site in the pentagonal ring. The effect of
native point defects on N dopants is quite strong: While the N doping is
endothermic in defect-free graphene, it becomes exothermic for defective
graphene. Our results imply that the native point defect and N dopant attract
each other, i.e., cooperative effect, which means that substitutional N dopants
would increase the probability of point defect generation and vice versa. Our
findings are supported by recent experimental studies on the N doping of
graphene. Furthermore we point out possibilities of aggregation of multiple N
dopants near native point defects. Finally we make brief comments on the effect
of Fe adsorption on the stability of N dopant aggregation.
