| Metal-nanotube heterostructures have attracted considerable interest due to their potential applications in catalysis, fuel cell technology, and hydrogen storage. We present a first-principles study of alkali metal atoms and clusters adsorbed on graphene and single-walled carbon nanotubes. In the case of single potassium atom adsorbed on graphene, we investigate adsorption energies and find that the disagreements reported in existing literature can be explained by long-range electrostatic interactions between the potassium atom and the graphene surface. We also investigate the optical properties of potassium atoms and clusters adsorbed on graphene and carbon nanotubes. The geometries, binding energies, and optical absorption spectra of the modeled structures are calculated in the framework of ab initio density-functional (DFT) and time-dependent density-functional (TDDFT) methods combined with the local-density approximation (LDA) and generalized-gradient approximation (GGA) for the exchange-correlation functionals. Our calculations show significant differences between the structures and absorption spectra of isolated alkali metal clusters and those adsorbed on graphene and carbon nanotubes. |
