No abstract

Density functional methods are used to calculate the band structure of an ideal and potassium-filled (8, 0) zigzag carbon nanotube. The calculations are performed taking account of the optimization of the parameters of the tube. It is shown that doping changes the characteristic bond lengths, and as a result of these changes the absorption spectra of the doped tubes are substantially different from those of the undoped tubes. The change of the character of the conductivity of a doped tube from semiconductor to metallic is largely due to the shift of the Fermi level. It is shown that doping decreases the frequency of the radial mode of the Raman scattering spectrum.

The methods of density functional theory are used to perform calculations of the band structure of a “zigzag” (12, 0) carbon nanotube, both ideal and filled with one-dimensional tetragonal crystalline potassium. The calculations take account of optimization of the structural parameters. It is shown that, in contrast to the case of a nanotube with a one-dimensional potassium chain, not only the surface of the nanotube but also its metal core conduct.

The electronic structure of two-dimensional silicon dioxide is studied using the projection augmented wave method within the density functional theory. The nonempirical calculations are significantly refined in the GW approximation. Nanofilms with a thickness of 0.35 to 1.76 nm, where the maximum number of atomic layer is 30, are considered. It is shown that the band gap strongly depends on the thickness of the two-dimensional nanocrystal and demonstrates three different types of behavior. This phenomenon is due to the shift of the Fermi level determined by the ratio of the numbers of Si and O atoms in the unit cell.