  Interwall interaction energies of double-walled nanotubes (DWNTs) with long
inner and short outer walls are calculated as functions of coordinates
describing relative rotation and displacement of the walls using van der Waals
corrected density functional theory. The magnitude of corrugation and the shape
of the potential energy relief are found to be very sensitive to changes of the
shorter wall length at subnanometer scale and atomic structure of the edges if
at least one of the walls is chiral. Threshold forces required to start
relative motion of the short walls and temperatures at which the transition
between diffusive and free motion of the short walls takes place are estimated.
The edges are also shown to provide a considerable contribution to the barrier
to relative rotation of commensurate nonchiral walls. For such walls,
temperatures of orientational melting, i.e. the crossover from rotational
diffusion to free relative rotation, are estimated. The possibility to produce
nanotube-based bolt/nut pairs and nanobearings is discussed.
