He Atoms Adsorbed in Carbon Nanotubes and Nanotube Bundles

We calculate the energetics of 4He and 3He atoms in the presence of one, two, and three carbon single-walled nanotubes (SWNTs). The spectrum is obtained for three characteristic sites: inside a tube in the presence of other tubes, within an interstitial channel, and in a groove. Calculations have been performed using both an axially symmetric averaged helium-carbon potential and for a potential constructed as a sum of individual carbon-helium interactions. Thermodynamic properties of helium atoms adsorbed in carbon nanonotube bundles are then studied using the single-particle spectrum. A range of one-dimensional (1D) to two-dimensional (2D) behavior is observed.