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(a) A hydrogen atom adsorbed on a CNT; the barrier for H diffusion to a nearby carbon site is over 1 eV. (b) and (c) Hopping of an H atom between two perpendicular CNTs that have the closest carbon atoms in registry at a distance d along the z direction [panel (b)], or off-registry, in which a shift s exists in the x direction for one of the CNTs [panel (c)].
Variation of energy along the transition paths for (a) the diffusion of H along a CNT, and (b) the hopping of an H atom between two perpendicular CNTs.
Cross-sectional view of the electronic charge distribution in a supercell containing two CNTs oriented perpendicular to each other [as in Fig. 1(c)] separated by a distance of d = 3.1 Å and a hydrogen atom at various points along the hopping pathway. Panel (a) corresponds to the initial state, (b)-(e) correspond to four (of the nine) intermediate states, and (f) to the final state.
Site PDOS for the carbon atom to which the hydrogen is initially bonded (C1, red line), the carbon atom to which H hops (C2, black line), and the hydrogen atom (H, blue line) at various stages along the hopping pathway between two perpendicular CNT’s separated by d = 3.1 Å (a) the initial state, (b) an intermediate state with H slightly closer to C2 than to C1, and (c) the final state. The vertical dashed (dotted) lines are a guide to the eye to show the bonding (antibonding) peaks that overlap. All the energies are relative to the Fermi level of each structure.
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