Density Functional Study of Defects in Boron Nitride Nanotubes

The electronic structure properties of two pristine and defected models of zigzag and armchair boron nitride nanotubes (BNNTs) are computationally studied. Chemical shielding (CS) tensors at the sites of various boron-11 (B-11) and nitrogen-15 (N-15) nuclei in each of the optimized structures are calculated and converted to isotropic and anisotropic chemical shieldings (ICS and ACS, respectively). The ACS values revel that boron atoms at the end of nanotube play the major role in determining the characteristic properties of the BNNTs. Defects are considered by removing a B-N bond from the pristine models yielding B-B and N-N bonds in the zigzag but not in the armchair BNNT. The changes of the CS tensors at the sites of those B-11 and N-15 nuclei in the B-B and N-N bonds are the most significant among other nuclei. The calculations are performed employing BLYP method and 6-31G* standard basis set using GAUSSIAN 98.