DFT, QTAIM, and NBO Study of Adsorption of Rare Gases into and on the Surface of Sulfur-Doped, Single-Wall Carbon Nanotubes

In this work, the interactions of S-doped single-wall carbon nanotubes (SCNTs) with rare gases (RGs) were fully considered using density functional theory (DFT), quantum theory of atom in molecule (QTAIM), and natural bond order (NBO) calculations. Different numbers of doped atoms and four RGs (He, Ne, Ar, and Kr) were considered for their adsorption on the surface of and into the SCNTs. The adsorption energies indicated that RGs could be adsorbed on the surface of the S-doped CNTs in endothermic process. Partial charges showed the small charge transfer from RGs to SCNTs. The calculated E-ad values showed that first He and then Ar are the best RGs for adsorption by SCNTs. QTAIM calculations confirmed the close-shell (non-covalent) interactions between SCNTs and RGs. In accordance with the results of QTAIM, both NBO charges and E2 interaction energies showed the interaction of SCNTs with RGs. Moreover, population analyses were performed to obtain electronic properties, reactivity parameters, and density of states plots of all structures.