Adsorption Configurations of Two Nitrogen Atoms On Graphene

We present calculations for different possible configurations of two nitrogen adatoms on graphene using the code VASP, based on Density Functional Theory (DFT). Two N atoms adsorbed on the graphene sheet can share a bond in two ways. They take positions either just above two adjacent carbon atoms or they form a bridge across opposite bonds of a hexagon in the graphene sheet. Both these configurations result into structural distortion of the sheet. Another stable configuration involving two N atoms consists of an N-2 molecule which is physisorbed at a distance 3.69 angstrom on the graphene sheet. Two N atoms can also be adsorbed on alternate bridge sites of neighbouring hexagons of graphene. This configuration again leads to distortion of the sheet in perpendicular direction.