van der Waals interaction in nanotube bundles:: Consequences on vibrational modes

We have developed a pair-potential approach for the evaluation of van der Waals interaction between carbon nanotubes in bundles. Starting from a continuum model, we show that the intertube modes range from 5 cm(-1) to 60 cm(-1). Using a nonorthogonal tight-binding approximation for describing the covalent intratube bonding in addition, we confirm a slight chiral dependence of the breathing mode frequency and we found that this breathing mode frequency increases by similar to 10% if the nanotube lies inside a bundle as compared to inside the isolated tube.