  Nano-diameter tubules made of folded graphitic sheets have drawn the
attention of physicists ever since the advent of fullerene research. These are
interesting because of their conductivity (depends upon chirality) as well as
their mechanical properties. Bunches of such tubes, single-walled and each of
same diameter (~14A), have been produced in the laboratory. In this work we
explore the mechanical properties of the bunch (hexagonal packing), having
assumed, for simplicity, uniform continuous distribution of carbon atoms on
each tube. The atom-atom potential (6-exp) is of Kitaigorodsky type where only
inter-tube interactions are considered. Intra-tube interactions are not
considered (implying a rigid tube model). This approximation works very well
for pure C60 solid. We find that the range of external modes is not well
separated from the radial mode frequency of the single tube as indicated by
measured data. Therefore interpretation of experimentally observed frequencies
needs to be done in terms of total modes of the bunch, including internal as
well as external modes. We have also studied pressure dependent deformations of
such a bunch which is found to be very interesting and is likely to provide
information about their mechanical strength.
