Electronic structure of short and long carbon nanotubes from first principles

First-principles calculations within the density-functional theory are carried out on carbon nanotubes with finite as well as infinite lengths. Quantum confinement effects, different from those in silicon clusters and carbon nanoparticles are predicted. It is shown that the electronic density of states of finite-length tubes resembles that of infinitely long tubes for tube lengths of only a few nanometers. A plot of the square of the wave function along the length of the tube shows periodic variation with a period of 0.4 nm, in agreement with recent measurements of I-V curves in short armchair tubes. [S0163-1829(99)02515-1].