The NMR Parameters of the C-Doped BN Nanotubes: A DFT Study

Ever since the carbon nanotube (CNT) was discovered by Iijima [1], the stable structures and the properties of non-carbon based nanotubes have intensively been investigated by numerous works; boron nitride nanotube (BNNT) has been introduced as an important member of this group[2–4]. Furthermore, in contrast to the non-polar CNTs, slight positive charge of boron atom (B) and slight negative charge of nitrogen atom (N) increase the polarity and the ionicity of the BNNTs. Therefore, the BNNTs have been proposed as more proper materials than the CNTs for applications in the specific electronic and mechanical devices. Previous studies have indicated that the properties of the electronic structure of the BNNTs are influenced by the doping atoms and impurities[5]. This computational work has investigated the properties of the electronic structure of the C-doped BNNTs by performing density functional theory (DFT) calculations of the NMR parameters. To this end, both representative models of armchair and zigzag BNNTs have been investigated. At first, the pristine and the C-doped structures have been allowed to relax by all atomic geometrical optimization. The chemical shielding tensors in principal axes system (PAS) are converted to measurable NMR parameters, chemical shielding isotropic (CSI) and chemical shielding anisotropic (CSA) by Eqs 1and 2. Subsequently, the isotropic and anisotropic chemical shielding (CSI and CSA) parameters have been calculated for the B, N, and C atoms present in both of the pristine and the C-doped structures. The results of structural properties, including bond lengths, energies, and band gaps, and NMR parameters have showed that With the replacement of carbon atoms instead of b, the values of the CSI increase for the pure nanotubes.