Using ab initio calculations, an investigation was made of the interaction of alkali metal atoms and alkali metal cations with perfect and defective carbon nanotubes. The results showed that the alkali metals preferred to interact with the pentagons and heptagons which appeared on the defective site of the carbon nanotube, rather than with the hexagons. The alkali metals always remained positively charged; independent of their charge state (neutral, cation) or the carbon ring with which they interacted. The molecular orbital energy level splitting from defect creation on the carbon nanotube, together with the localization of charge-electron density on the defect, resulted in more efficient binding of the alkali metals. Metallic sodium appeared to bind very weakly to the nanotube, when compared with the remainder of the alkali metals. The Na anomaly was attributed to the fact that, unlike K, the Na inner p-shell was energetically lower than the nanotube’s molecular p-orbitals. As a result, the Na p-shell was essentially excluded from any binding-energy contribution. In the alkali metal cation case, the electronegativity trend was followed.

Why Alkali Metals Preferably Bind on Structural Defects of Carbon Nanotubes: a Theoretical Study by First Principles. G.Mpourmpakis, G.Froudakis: Journal of Chemical Physics, 2006, 125[20], 204707