In addition to the exceptional physicochemical properties associated with single wall carbon nanotubes (SWNTs), they also have become the major subjects of numerous theoretical investigations [1]. On the theoretical side, an important aspect of SWNT properties is related to the nanotube-gas interaction [2]. This is due to the fact that studies related to the adsorptions of various gases on carbon nanotubes have explored different aspects of nanotube adsorbate interactions [3]. Some researchers have found that exposure to O2, NO2 or NH3 dramatically influences the electrical resistance and thermoelectric power of semi-conducting SWNTs [4]. On the other hand, for some gases such as CO, an applicable SWNT based sensor has not yet been reported [5]. In addition to its effect on the carbon gasification processes [6], carbon monoxide has an important role in different synthetic approaches of carbon nanotubes [7-9]. Christopher and Bradley [10] have studied the adsorption of CO on SWNTs using Fourier transform infrared spectroscopy. Mann et al. [11] have used semi-empirical direct dynamics simulations to study the potential role of CO in the gas-phase catalytic growth of carbon nanotubes. In all of these processes, CO is primarily physisorbed on SWNT. Therefore, to understand the effect of CO on the electronic and transport properties of carbon nanotubes, we theoretically studied adsorption of CO molecules on the SWNTs.
