Study of noncovalent interactions of end-caped sulfur-doped carbon nanotubes using DFT, QTAIM, NBO and NCI calculations

In the current study, the interactions of carbon nanotube and sulfur-doped carbon nanotubes (SCNTs) with methanol, methanethiol, water and dihydrogen sulfide at on-body and dead-end positions of nanotubes have been studied. Interaction energies in the gas and solvent (via PCM model) were calculated using density functional theory calculations. Atomic charges, interaction energies, electron densities and their Laplacians at bond critical points have been calculated. Moreover, noncovalent interaction isosurfaces have been visualized using NCI index calculations. Interactions in gaseous phase were more favorable than those in solvent phase, and among considered solvents (benzene, chloroform and cyclohexane), cyclohexane showed the most preferred interactions. In addition, oxygen-bearing molecules (methanol and water) showed more favorable interactions compared with sulfur-bearing ones. NBO analyses revealed the stronger donor-acceptor interactions with methanol and methanethiol. QTAIM calculation results indicated the reasonable electron densities at BCPs, and the Laplacians of electron densities showed ionic-like (closed shell) interactions. Moreover, isosurfaces of these interactions were also studied to depict the interaction surfaces, and DOS plots for SCNTs were obtained to define their HOMO-LUMO levels and electric conduction properties. The increasing of the global softness and decreasing of total hardness was resulted by sulfur doping of nanotubes, which causes the heterodoped nanotubes to become less electrophilic species.