Carbon nanocones: A variety of non-crystalline graphite

Previously known graphitic structures of conical shape - whiskers and helical cones - consist of a single wrapped graphene sheet, which gives a rather amorphous tip structure. Carbon nanocones, on the other hand, are nearly perfect sheets, curved by 1-5 pentagonal rings in the otherwise hexagonal network of carbon atoms. However, the resulting loss of periodicity implies electronic properties quite different from those of graphite and nanotubes. Experimental results have so far been limited by restricted access to sample material, but the cones have shown a unique capability of storing hydrogen gas reversibly at normal temperatures. The cones are characterized by large electrostatic dipole moments which will influence future experiments and technological applications. In this paper we study the interplay between topology, geometry and electronic properties, and investigate the magnitude of the dipole moments as a function of size and apex angle of the cones. (c) 2008 Elsevier B.V. All rights reserved.