Bulk and Lattice Properties for Rigid Carbon Nanotubes Materials
  We use an atom-atom potential between carbon atoms to obtain an interaction potential between nanotubes (assumed rigid), thereby calculating the cohesive energy of a bunch of nanotubes in hexagonal two dimensional packing. The model proposed is quite similar to our earlier work on fullerenes and organic molecular crystals. The results for inter-nanotube distances, energy per unit length, bulk modulus and phonons for inter-nanotube vibrations are obtained and compared with available data from measurements and other available calculations. We also model formation of multi-wall nanotubes. We find the results for various calculated quantities agreeing very well with measured structural parameters and other calculations. The reversible energy stored on compression of the bunch of nanotubes on application of pressure up to 30 Kbar calculated in this rigid molecule model is overestimated by about 30% when compared with measured results, signifying the appreciable flexibility of tubes at high pressures. The model is considered very suitable for incorporating flexible nanotubes in bunches of single and multi-wall nanotube materials of various types. 
V.K. Jindal, Shuchi Gupta and K. Dharamvir