Theoretical explorations on BN-doped armchair single-walled carbon nanotubes

The geometries and stabilities of mono-BN doped (5,5) armchair single-walled carbon nanotube (ASWCNT) isomers for a smaller C50H20 model are first investigated by both AM1 and HF/4-31G methods. The calculations suggest that both the two methods obtain similar results, demonstrating that the AM1 method is reliable in calculating the properties of BN-doped ASWCNT isomers. Then, the equilibrium structures and relative stabilities of the mono-, di-, and tri-BN doped isomers for a larger (5,5) ASWCNT model (C110H20) are further studied based on AM1 level. For mono-BN doped ASWCNT, the thermodynamic stabilities of its isomers in general decrease with the separation between two heteroatoms, and the isomer with two neighbored B and N atoms is the most stable one. For di- or tri-BN doped ASWCNT isomers, the N-N and B-B bonds should be avoided and the isomer with a B-N-B-N or B-N-B-N-B-N chain in same hexagon is the most stable one. The BN-doping generally enhances the redox and electron excitation properties of BN-doped ASWCNT isomers compared with their host tube, and their stabilities increase with their diameter enlargement on the whole.