Ab initio study of curvature effects on the physical properties of the Xe-doped nanotubes and nanoropes

A systematic comprehensive ab initio investigation of the energetics, structural, electronic, and optical properties of weakly and heavily Xe-doped ultrathin 4 A and large-diameter carbon nanotubes has been performed. The contributions of the dispersion as well as the zero-point energies have been considered. The effects of the tube diameter and the different chiralities of the carbon nanotubes on the adsorbant-induced physical properties have been investigated. The favoured tubes for Xe atom adsorption are armchair (n, n) tubes, and one may not observe any appreciable surface Xe adsorption on zigzag (n, 0) or chiral (m, n) tubes. The band gap of a semiconducting achiral zigzag nanotube is reduced whereas the band gap of a chiral semiconducting tube is enhanced by the adsorption of Xe atoms. Xe adsorption in/on the metallic tubes creates extra (one or more) conductive channels which run inside/outside the nanotubes and may result in quite enhanced conduction. The optical absorption of the achiral (chiral) 4 angstrom diameter tube is considerably changed (unchanged) by the adsorption of the Xe atoms. The calculated peaks in large-diameter pristine nanotubes have been detected in the experimental measurements. In the (10, 0) and (10, 10) nanotubes, the small adsorption of Xe does not change the optical absorption of the pristine tube. The computed binding energy and the saturation Xe concentration are in reasonable agreement with the experimental data available for the (10, 10) nanotube.