Nuclear Magnetic Response Parameters Of SiO2Nanotube And BN Nanotube

In this thesis, at the first step, the geometry structure of SiO2nanotube and BN nanotube and BN nanoribbons were optimized using the density function theory based on B3LYP method under the6-31G (d) basis set. Secondly, we study the electronic structures and properties of each structure based on gauge included atomic orbital (GIAO) approach. The research work includes the following two aspects:1. Influence of the size effect on the Chemical Shielding Tensors of SiO2nanotubesFinite length SiO2nanotubes composed of a three-membered ring (3MR) cross section were investigated by density functional theory, but Nuclear Magnetic Resonance (NMR) results reveal that the isotropic chemical shielding tensor (σiso) and anisotropic chemical shielding tensor (Aa) of the SiO2nanotubes oscillate from the terminal end to the intermediate part of the structures with an increase in nanotube lengths, and they tend to reach different stable values. When the length is greater than certain value the σiso and Δσ values obtained from the intermediate part of the finite length nanotube can be used for theoretical predictions of long or infinite length nanotubes. Hence, this investigation is a guide for the selection of reasonable finite length nanotubes to model infinite length nanotubes.2. Nuclear Magnetic Response of the armchair BN nanotube and BN nanoribbonsFinite length BN nanotubes composed of three-membered ring (3MR) cross section have been investigated by density function theory. The NMR results reveal that the isotropic chemical shielding (σiso) and anisotropic chemical shielding (Δσ) of BN nanotubes oscillate from the terminal end to intermediate part of the structure with increasing of nanotube lengths, and trends to reach different stable values. As the length is greater than certain value, the isotropic chemical shielding (σiso) and anisotropic chemical shielding (Δσ) obtained from intermediate part of finite length nanotube, can be used to be theoretical prediction for longer or infinite lenthe nanotubes. Hence, this investigation is a guide for selecting reasonable finite length nanotube to model infinite length nanotube. Afterwards, reasonable finite length BN nanotubes with different diameters were calculated using the density functional theory at B3LYP/6-311G**level. It was found that the NMR parameters of the intermediate part of nanotube were inversely proportional to the diameter and diameter square. In addition, as the nanotube diameter increase, the chemical shielding tensors of11B and15N in the middle layers of BN nanotubes were rapidly meet the values calculated for graphitic BN nanoribbons.