Density-functional study of the mechanical and electronic properties of narrow carbon nanotubes under axial stress

The behavior of some narrow single-wall carbon nanotubes under uniaxial stress was studied. The first principles local density-functional calculations were carried out using helical repeat units and periodic boundary conditions for a single infinite chain. The mechanical response of the tube, the geometrical deformations, and the axial elastic modulus are calculated. The mechanical deformations are reflected also in the electronic properties. The change of the band gaps of the chiral tubules under axial stress was investigated. The indirect gaps of $\sim 0.1\mathrm{eV}$ can be closed applying small $(<5\%)$ deformations which results in semiconductor-metal transitions.

Figure 1

The geometrical parameters used in the characterization of the zigzag (top left), the armchair (top right), and the chiral (bottom) nanotubes.

Figure 2

Highest valence and lowest conduction helical 1D bands of (5,2) SWNT. Upper figure: TB bands derived from graphene. Graphitic special points are indicated. Lower figure: Single chain DFT calculations.

Figure 3

The indirect band gap (upper panel) and the three nonequivalent bond lengths (lower panel) of the (5,2) SWNT as a function of strain.