First-Principles Calculation of 13C NMR Chemical Shifts of Infinite Single-Walled Carbon Nanotubes: New Data for Large-Diameter and Four-Helical Nanotubes

By using the density functional theory method, we calculate the 13C NMR isotropic chemical shifts of the semiconducting and semimetallic infinite single-walled carbon nanotubes (SWNTs). We find that the 13C chemical shifts of SWNTs with the diameter smaller than 1.4 Å can be classified into two distinct groups according to their electronic structures: the semiconducting group and the semimetallic group. The chemical shifts of the semiconducting group decrease monotonously with the increasing nanotube diameter, and are 0−12 ppm strikingly larger than those of their semimetallic counterparts in the typical diameter range (1.05 ± 0.2 nm) of SWNTs produced by the common high-pressure CO decomposition method (HiPCO). The chemical shifts of the two groups overlap around the diameter of 1.4 Å. Then the chemical shift of the semimetallic group becomes larger than that of the similar-sized semiconducting group as the diameter is larger than 1.4 Å. The chemical shifts of the four examined helical SWNTs are very close to those of the zigzag SWNTs with similar diameters and electronic structures.