DFT study on influence of Si and Ge doping on the chemical shielding tensors in the armchair AlN nanotubes

To investigate the influence of Si and Ge doping on electrostatic structure properties, we considered an armchair model of (4, 4) aluminum nitride nanotubes (AlNNTs) of 1 nm length, consisting of 32 Al and 32 N atoms. The mouths of the nanotubes are capped by hydrogen atoms in order to saturate the dangling bonds of the boundaries, to simulate a longer tube and to decrease calculation time. The calculated chemical shielding (CS) tensors are converted to isotropic and anisotropic CS. The results show that in both models of Si- and Ge-doped AlNNTs, among all N atoms those that are directly connected to Si and Ge atoms have the smallest isotropic and anisotropic chemical shielding. The calculations are performed at the level of the density functional theory (DFT) using a Gaussian 03 package of program.