Uniform curves for van der Waals interaction between single-wall carbon   nanotubes
  We report very simple and accurate algebraic expressions for the van der Waals (vdW) potentials and the forces between two parallel and crossed carbon nanotubes. The Lennard-Jones potential for two carbon atoms and the method of the smeared out approximation suggested by L.A. Girifalco were used. It is found that interaction between parallel and crossed tubes are described by different uniform curves which depend only on dimensionless distance. The explicit functions for equilibrium vdW distances, well depths, and maximal attractive forces have been given. These results may be used as a guide for analysis of experimental data to investigate interaction between nanotubes of various natures. 
Evgeny G. Pogorelov, Alexander I. Zhbanov, Yia-Chung Chang