First-principles studies of zigzag pristine boron nitride nanotubes doped with one iron atom

Interaction of one iron atom with pristine zigzag boron nitride nanotubes with different diameters, ranging from (8,0) to (12,0), have been investigated using density functional theory calculations. Departing from four initial configurations, considering each of them interacting with the tubes’ walls either from inside or outside, we have analyzed the adsorbate migration to the most favorable positions together with the related binding energies and the equilibrium distances as well as the electronic structure of the final systems. It was observed that the smaller the radius of the tube the lower is the binding energy for all studied structures, and also that the inner configuration is more stable than the outer one for small radius. For the preferred position for the iron atom, it was seen that it varies according to the starting configuration and that the iron-first-nitrogen-neighbor bond length works as a constraint in determining the most favorable position for the adsorbate. Finally, for the electronic structure, it was observed that the presence of the dopant introduces localized levels at the band gap of the nanotubes and that those levels are mostly related to the orbitals 3d and 4s of the iron atom. For the inside case, as a consequence of higher hybridization and a confinement effect, the gap closure is more pronounced for small diameter tubes. For all studied structures, it was observed a net-spin-polarization equal to 4 μ _B.