Density functional calculations on 11B and 15N chemical shielding tensors of small boron nitride nanotubes and graphitic sheet

Geometrical structure, nuclear magnetic resonance (NMR) chemical shielding tensors, and chemical shifts of boron and nitrogen nuclei are investigated for five small boron nitride nanotubes (BNNTs, three zigzag and two armchair types) and boron nitride (BN) sheet using density functional theory (DFT) level of theory. Geometrical structures of BNNTs are studied regarding B–N bonds and dihedral angles of B and N vertices in both zigzag and armchair nanotubes. Bond lengths are approximately constant while dihedral angles vary in different BNNTs and along the tubes, tending to resemble those of BN sheet. It is also shown that all NMR parameters remain constant along the tube and could be considered as appropriate tools for characterization of small BNNTs. Studies revealed that calculated chemical shielding and chemical shifts of 11B and 15N nuclei are in complete accordance with those of hexagonal BN (hBN). However, NMR parameters vary with the tube diameter. Chemical shielding tensors of 11B and 15N increase and chemical shifts decrease with increase in the diameter of tubes and rapidly meet the values calculated for BN sheet. Therefore, it can be concluded that BNNTs, specifically large ones, have approximately constant NMR chemical shielding tensors and chemical shifts.