Ab initio study of carbon nanotubes in electric fields

Electronic structures of four types of carbon nanotubes in an electric fiel d have been investigated by the ab initio pseudopotential plane wave method . The local field enhancement at the tips of nanotubes and the screening of the electric field inside the nanotubes are considerable for nanotubes wit h a small gap between the highest occupied band (HOB) and the lowest unoccu pied band (LUB) in the electronic states. The dangling bond (DB) states nea r the HOB localized at the edge of nanotubes are significantly influenced b y the electric field. Thus, the present results strongly suggest an importa nt role of the localized states of conducting nanotubes with small electron ic gaps in field emissions.