Ab initio study of toroidal carbon nanotubes with encapsulated atomic metal loops

Toroidal carbon nanotubes can serve as hosts for encapsulated loops of atomic metal wires. Such composite structures have been analyzed using density functional theory for a semiconducting C-120 torus encapsulating chains of Fe, Au, and Cu atoms. The sheathed metal necklaces form a zigzag structure and drop the highest occupied molecular orbital and/or lowest unoccupied molecular orbital band gap to less than 0.1 eV. The iron composite is ferromagnetic with a magnetic moment essentially the same as that of bcc iron. The azimuthal symmetry of these toroidal composites suggests that they may offer novel electromagnetic properties not associated with straight, metal-encapsulated carbon nanotubes.