In this paper, electronic structures of a series of dimension- variational single- walled carbon nanotubes are investigated by use of the first-principles calculations. The density of states and the variation of density of states with the tubular radius R obtained are in good agreement with the experimental results. The value of density of states at the Fermi level is reduced with increasing tubular radius R, which shows the chemical reactivity of carbon nanotubes is strengthened. The bonding between C-C in nanotubes is distorted σ and π bonds consisting of 2s, 2p valence electrons. As the tubular radius R increases, the curvature of the chemical bonds is reduced, the bonding between C-C and binding energy are increased, electronic density and the corresponding potential field are reduced. The above results show the nanotubes with small size have advantage in the syntheses of nanometer-scale composites.

Key words: ELECTRONIC STRUCTURE, NANOPHASE MATERIALS, CHEMICAL BONDS