Study Of Hypothetical Silicon Nanotubes Formed By Rolling Up Graphite-like Silicon Layers

Nano-materials are 'the most promising materials' in this century. On the other hand, the 1st-principle calculations have become the fundamental of computational materials science these years. Using 1st-principle calculations to study the properties of nano-materials has been the focus of current researches.Considering the successful preparation and researches of carbon nanotubes, silicon-based nano-materials are expected to have great possible application potential in future nano electronic devices. As shown in this paper, employing the 1st-principle SIESTA program based on density functional theory, we study the hypothetical silicon nanotubes which could be formed by rolling up graphite-like silicon layers, and do the following work:1. Owing to their great importance in SIESTA calculations, the norm-conserving pseudopotentials based on density functional theory for silicon and iron atoms are chosen and verified, and the numerical atomic orbital basis dealing with them within SIESTA program are constructed and verified.2. The geometry structures of (5,5) and (5,0) hypothetical silicon nanotubes are optimized. The results show that the bond lengths are between 2.234 A and 2.239 A, 2.242 A and 2.246 A, respectively. The electronic structures are calculated for both nanotubes, showing both Fermi levels crossed by energy bands, indicating metallic characteristic.3. The effect of vacancy on (5,5) hypothetical silicon nanotube is studied, showing that the nanotube with a vacancy percentage of 1% collapse to an non-tube structure. In contrast, (5,5) carbon nanotube with the same vacancy percentage has only a slightdeformation, with bond lengths around the vacancy changed.4. The geometry structure of (5,5) hypothetical silicon nanotube filled with iron atom is optimized. The nanotube is found undergoing small dilation, with bond lengths between 2.242 A and 2.250 A. The density of states and magnetic moment are calculated, showing that this structure is metallic and has a net magnetic moment of 4.18μ_B.