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The effective parameters of (5, 0) and (5, 5) single-wall carbon nanotubes during the interaction with carbon dioxide as sensors are determined. The interaction of carbon dioxide  molecules with internal and external walls of the nanotubes is studied using Gaussian 03 coding by density functional theory (DFT) at the B3LYP/6-311G level of theory. CO2 rotation around tube axles vertically and parallel to the internal and external walls has been investigated. The carbon dioxide molecule is predicted to bind only weakly to nanotubes, and the tube-molecule interactions can be identified as physisorption. CO2 adsorption is stronger on external wallsthan on internal walls, and adsorption on the external wall of (5, 0) is stronger than on the external wall of (5, 5); the adsorption energies are exothermic and equal to -0.8884 and -0.0528 kcal/mol, respectively. The rotation energy barrier for (5, 5) is lower than that for (5, 0) in all rotations, therefore in these interactions (5, 5) is more active. The energy gap significantly changes in the presence of  carbon  dioxide molecules on the inside surface of (5, 0) and the electric conductivity is affected, but no remarkable change is observed in the electronic structure of (5, 5).