Ab initio study of the interactions between boron and nitrogen dopants in graphene

We present a first-principles computational study of the interactions between the boron (B) and nitrogen (N) dopant atoms in graphene. Our calculations are carried out using density functional theory combined with the generalized gradient approximation for the exchange-correlation functional. The total energies, equilibrium geometries, electronic charge distributions, and densities of states of doped graphene sheets are examined in cases of B$−$B, N$−$N, and B$−$N co-doped graphene. We find the B$−$B and N$−$N interactions to be repulsive and the B$−$N interaction to be attractive. In all cases studied, dopant-dopant interactions appear to have a relatively short range. The interaction energy between the two dopant atoms is found to be inversely proportional to the square of the separation distance. We interpret these results in terms of donor-acceptor interactions and structural relaxation. The strong bonding between the B and N atoms indicates the possibility of the formation of isolated patches of hexagonal boron nitride in B$−$N co-doped graphene.