  Ab-initio calculations have been performed to study the geometry and
electronic structure of boron (B) and nitrogen (N) doped graphene sheet. The
effect of doping has been investigated by varying the concentrations of dopants
from 2 % (one atom of the dopant in 50 host atoms) to 12 % (six dopant atoms in
50 atoms host atoms) and also by considering different doping sites for the
same concentration of substitutional doping. All the calculations have been
performed by using VASP (Vienna Ab-initio Simulation Package) based on density
functional theory. By B and N doping p-type and n-type doping is induced
respectively in the graphene sheet. While the planar structure of the graphene
sheet remains unaffected on doping, the electronic properties change from
semimetal to semiconductor with increasing number of dopants. It has been
observed that isomers formed differ significantly in the stability, bond length
and band gap introduced. The band gap is maximum when dopants are placed at
same sublattice points of graphene due to combined effect of symmetry breaking
of sub lattices and the band gap is closed when dopants are placed at adjacent
positions (alternate sublattice positions). These interesting results provide
the possibility of tuning the band gap of graphene as required and its
application in electronic devices such as replacements to Pt based catalysts in
Polymer Electrolytic Fuel Cell (PEFC).
