  We calculate the interaction energy and force between atoms and molecules and
single-walled carbon nanotubes described by the Dirac model of graphene. For
this purpose the Lifshitz-type formulas adapted for the case of cylindrical
geometry with the help of the proximity force approximation are used. The
results obtained are compared with those derived from the hydrodymanic model of
graphene. Numerical computations are performed for hydrogen atoms and
molecules. It is shown that the Dirac model leads to larger values of the van
der Waals force than the hydrodynamic model. For a hydrogen molecule the
interaction energy and force computed using both models are larger than for a
hydrogen atom.
