Energetics and electronic structure of a single copper atomic chain wrapped in a carbon nanotube:a first-principles study

In the generalized gradient approximation, the energy and electronic structure are investigated for a single copper atomic chain wrapped in （4, 4）, （5, 5） and （6, 6） armchair carbon nanotubes by using the first-principles projector-augmented wave potential within the framework of density functional theory. The results show that the （4, 4） and （5, 5） tubes are too narrow to wrap a Cu chain, but the （6, 6） tube is nearly ideal to wrap a Cu chain on its centre axis. Wider tubes are anticipated to wrap more than one Cu chain spontaneously with forces amounting to a fraction of a nanonewton. Although the tube-chain interaction decreases with the increase of the tube diameter of （4, 4）, （5, 5） and （6, 6） successively, the charge density of the Cu@（6, 6） combined system still does not show complete superposition of that of the pristine （6, 6） tube and Cu chain. Successively reducing the restrictions of （4, 4）, （5, 5） and （6, 6） tubes on the Cu chain leads to a reduction in shift of the highest peak of the Cu chain towards lower energies, that is from -0.5177 eV of the isolated Cu chain to -1.36785 eV, -0.668 eV and -0.588 eV for the Cu@（4, 4）, Cu@（5, 5） and Cu@（6, 6） systems, respectively. In reverse, the strong metallic character of the Cu chain also enhances the metallic character of the combined systems so that the broader pseudogaps of the pristine carbon nanotubes around the Fermi level change into the narrow pseudogaps of the combined systems.