Abstract Submitted to the    NANOTUBE'04 Conference:

Based on first-principles calculations, we study the electronic structure of double-walled carbon nanotubes(DWCNTs), especially when the diameter of the inner tube is less than 5.5 A. Our model system, (7,0)@(17,0), may be grown exothermically and is composed of two semiconducting nanotubes. Large curvature of the inner tube induces s^*-p^* hybridized band near the Fermi level and the DWCNT becomes metallic by band-crossing of the s^*-p^* inner-tube band and the p outer-tube band. We investigate the changes of electronic structure near the Fermi level by the adsorbates on the outer tube. We also find that the energy gap of composite double-walled nanotube, which consists of boron nitride nanotube and carbon nanotube(CNT), is modified from that of the original CNT due to radial distortion.