Modeling the effect of dispersed doping agents in carbon nanotubes

Theoretical studies of how the electronic properties of a nanotube are affected by one isolated doping agent is commonly done by ab-initio electronic structure calculations. Although these calculations are essential to understand how the system responds to doping, they are by no means sufficient, since, in reality, a large disordered array of doping agents must be considered. It is then necessary to combine ab-initio techniques with less-computationally-demanding methods if one wishes to describe the real effect of doping on the electronic properties of nanotubes. Here we propose a method that makes use of ab-initio results for single impurities as an input to generate the parameters of the less-demanding tight-binding technique. The method is based on suitable sum rules for the Green functions of the impurity-free nanotubes and does not rely on any fitting scheme. The resulting parametrization allows us to describe disordered systems without losing the important contributions due to charge transfer and screening. Transport properties are subsequentially investigated.