AbstractWe investigate the insertion of halide and alkali atoms into narrow single‐walled carbon nanotubes with diameters <9 Å by density functional theory; both chiral and non‐chiral tubes are considered. The atoms are stored in the form of ions; the concomitant charge transfer affects the band structure and makes originally semiconducting tubes conducting. The electrostatic interaction between a charge and the walls of the tube is explicitly calculated. The insertion energies and the positions of the ions are determined by a competition between electrostatic energy and Pauli repulsion. For comparison, we consider ions in gold nanotubes. Alkali ions follow the same principles in gold as in carbon tubes, but chloride is specifically adsorbed inside gold tubes.