van der Waals and Casimir interactions between atoms and carbon nanotubes

The van der Waals and Casimir interactions of a hydrogen atom (molecule) with a single-walled and a multi-walled carbon nanotubes are compared. It is shown that the macroscopic concept of graphite dielectric permittivity is already applicable for nanotubes with only two or three walls. The absorption of hydrogen atoms by a nanotube at separations below 1 nm is considered. The lateral force due to exchange repulsion moves the atom to a position above the cell center, where it is absorbed by the nanotube because the repulsive force cannot balance the van der Waals attraction.