Modelling the effect of randomly dispersed adatoms on carbon nanotubes

Abstract

Theoretical studies of how the electronic properties of carbon nanotubes are affected byforeign adsorbed atoms are commonly done by ab initio electronic structure calculations inwhich a single impurity atom is considered. Although these calculations are essential tounderstand how the system responds to doping, they are by no means sufficient, since, inreality, a large disordered array of adatoms must be considered. It is then necessary tocombine ab initio techniques with less computationally demanding methods if one wishes todescribe the real effect of doping on the electronic properties of nanotubes. Here we proposea method that makes use of ab initio results for single impurities as an input to generatethe parameters of the less demanding tight-binding technique. It is based on suitable sumrules for the Green functions of the impurity-free nanotubes and does not relyon band-structure fitting. The resulting parameterization allows us to describedisordered systems without missing the important contributions due to chargetransfer and screening. The method is illustrated with hydrogen atoms adsorbed toa nanotube, for which the transport properties are subsequently investigated.