Structures And Electronic Properties Of Infinite Single-Walled MgO Nanotubes

One-dimensional nanomaterials have been the subject of experimental and theoretical researches since carbon naonotubes were discovered. It is important to study nanotubes and nanowires for nanotechnology. Becides carbon nanotubes, more nanotubes have been synthesized, such as GaN, ZnO, BN nanotubes. As a typical II-VI metal oxide, the electronic structures of MgO have been attracted a lot of attention. MgO is a wide bandgap insulator. During past decades, MgO of different dimensions and scales have been widely researched both experimentally and theoretically. Numerous MgO nanostructures have been achieved. For example, nanorods, nanobelts, nanowires and nanotubes. This thesis is arranged as following two parts:1. Structural characteristics of zigzag and armchair MgO nanotubesIn this work, we investigate the structure and electronic properties of one-dimensional infinite-length single-walled zigzag and armchair MgO nanotubes using density-functional theory (DFT) and 6-31G(d) basis set. Average bond length, binding energy, Mulliken charge, energy gap and density of states have been discussed. The energy gap and binding energy monotonically increased with the increasing of tube diameters. The Mulliken charge analysis has been performed. The Mulliken charge of oxygen atoms show that the charge transfer from magnesium to oxygen is less than 2e. Obviously, the mixed ionic and covalent bonding exists in these MgO nanotubes. There are two types calculated geometrical parameters of Mg-O bonds:along the tube circumference (a1) and along the tube axis (a2). The bond length a1and a2 decrease as the tube diameters increase. In addition, the average bond length a1 of MgO nanotubes are slightly longer than a2. This is maybe because of the difference about electronic density between two directions.2. The investigation of other MgO nanotubesThe PBC-DFT method calculation is implemented in the Gaussian 03 program package. All unit cells were generated by TubeGen 3.3, each of them contains four or two layers of atoms. Using the PBC model, we extent the supercell along the tubular axis to infinite length. For chiral MgO nanotubes, the energy gap and binding energy monotonically increased with the increasing of tube diameters. The energy gap and binding energy can reflect the chemical activity and stability of different structures. The Mulliken charge analysis show that the charge transfer from magnesium to oxygen is less than 2e. We can see covalent bond dominate in chiral MgO nanotubes more obviously than zigzag and armchair nanotubes.In this work, we also investigate the (MgO)n nanotubes using density-functional theory and 6-31G(d) basis set. Using the PBC model, we extent the supercell along the tubular axis to infinite length. All unit cells were generated by two layers of atoms. Different from other nanotubes, the energy gap decreased with the increasing of tube diameters. Structural stability decreased with the increasing of tube diameters. Mixed covalent and ionic bonding property exist in (MgO)n nanotubes.