Screening of ions in carbon and gold nanotubes — A theoretical study

• The image charge compensates for the loss of solvation.
• The Coulomb potential of the ions is strongly screened.
• Gold nanotubes screen better than carbon nanotubes.

We examine the insertion of alkali ions into narrow nanotubes of graphite and gold by density functional theory. The surrounding tubes screen the ionic charge very effectively; the resulting image energy compensates well for the loss of solvation. In addition, ion–ion interactions are strongly reduced. These effects are stronger for gold than for graphite tubes. Our results explain at an atomic level, why narrow tubes store charge so effectively.

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