Adsorption,absorption and diffusion pathways of nitrogen are studied for ferromagnetic body-centered cubic iron via spin-polarized density functional theory in combination with the climbing image nudged elastic band method.The computed data suggest that,depending on the coverage of N atoms,N prefers to stay on particular surface sites.Once pinned down well below the surface,N prefers to move into octahedral interstices rather than tetrahedral interstices.However,the tetrahedral interstices are crucial because they act as transition states and yield the saddle point energies of the corresponding minimum energy pathways.In comparison with carbon,we found that nitrogen prefers a different pathway from the(1 0 0)surface to the subsurface due to its strong repulsive interaction with Fe ions.
