Modeling of molecular hydrogen and lithium adsorption on single-wall carbon nanotubes

Adsorption of lithium and hydrogen onto carbon nanotubes has been modeled using a neglect of diatomic differential overlap semiempirical calculation. Our results predict that lithium can be adsorbed on zig-zag nanotubes with a charge transfer, an adsorption energy, and a vibration frequency which depend on the tube radius and whether the adatom approaches the surface from outside (exo-way) or inside (endo-way). Adsorbed lithium allows the anchoring of molecular hydrogen on the carbon nanotube with a binding energy in a chemisorption regime compared to previous experimental and theoretical works which show that ${\mathrm{H}}_2$ is physisorbed. We also predict that a shift of the hydrogen stretching mode upon adsorption should be observable experimentally by vibrational spectroscopy.