Electronic structure, energetics and geometric structure of carbon nanotubes: A density-functional study

Based on the local density approximation (LDA) in the framework of the density-functional theory, we study the details of electronic structure, energetics and geometric structure of the chiral carbon nanotubes. For the electronic structure, we study all the chiral nanotubes with the diameters between 0.8 and 2.0 nm (154 nanotubes). This LDA result should give the important database to be compared with the experimental studies in the future. We plot the peak-to-peak energy separations of the density of states (DOS) as a function of the nanotube diameter (D). For the semiconducting nanotubes, we find the peak-to-peak separations can be classified into two types according to the chirality. This chirality dependence of the LDA result is opposite to that of the simple π tight-binding result. We also perform the geometry optimization of chiral carbon nanotubes with different chiral-angle series. From the total energy as a function of D, it is found that chiral nanotubes are less stable than zigzag nanotubes. We also find that the distribution of bond lengths depends on the chirality.