Electronic properties of single-walled silicon nanotubes compared to carbon nanotubes

Using the first principles method, we have investigated the electronic properties of Si-based single-walled nanotubes with different diameters and chiral vectors. The electronic properties show significant difference with those of carbon nanotubes. Si gearlike nanotubes (g-NTs) are more stable according to the formation energies, as Si atoms prefer the sp(3) hybridization. Si (n,n) (n=5-11) g-NTs are semiconductors, whose gaps decrease as the diameters increase. Si (n,0) (n=10-24) g-NTs are semiconductors and the gaps decrease in a period of 3. The results for large Si g-NTs can be explained using the tight-binding model and the method of Brillouin zone foldings. The (n,0) (n=5-9) tubes are metal due to the sigma(*) and pi(*) mixing, which is rather strong for the small tubes.