Edge states in horseshoe-shape carbon nanotubes transformed by hydrogen adsorption

We have investigated hydrogenated single-wall armchair (n,n) carbon nanotubes (CNTs) with 4≤n≤12 by using density functional theory calculations. Hydrogen adsorption may transform the CNTs into a horseshoe shape. Nonmagnetic edge-localized electron states have been identified in CNTs of horseshoe shape in this work. The σ-bond-like orbital overlaps across the edge-localized electrons, which sustain the horseshoe shape of the CNTs and hinder spontaneous unravelling into a graphene nanoribbon, cause the horseshoe-shape CNTs to become nonmagnetic metal. The bonding energy between the hydrogenated edges increases with the CNT diameter, approaching a limit of ∼1 eV.