The shielding tensor in 13 C nuclear magnetic resonance (NMR) offers important information about the structural aspects of carbon materials from a local point of view. Not only the symmetry of the carbon site but also the presence of local structural distortions can affect the values of the isotropic shielding constant, the shielding anisotropy, and the deviation from axial symmetry. In this report, the 13 C shielding in a single graphene sheet was calculated using density functional theory (DFT) via the gauge-including projector augmented plane wave (GIPAW) method. After performing convergence tests involving changes of k sampling and supercell size, the calculations were extended to graphene-based systems, including graphene bilayer and stacked graphene sheets, finally leading to hexagonal graphite. The calculated results showed good agreement with experimental values obtained by 13 C NMR measurements in different types of carbon materials, evidencing the power of the DFT calculations for predicting NMR parameters in graphene-based nanocarbons.

The 13 C NMR chemical shifts corresponding to di↵erent sites in atomistic models of disordered carbons were computed at di↵erent H contents by employing DFT calculations. Structural models were generated by molecular dynamics simulations and validated by the pair distribution functions; further bonding analyses were carried out to determine the amount of sp 3 and sp 2 carbons in the structures. Specifically, the obtained results allow the distinction of the chemical shifts associated with di↵erent types of carbon sites, with di↵erent hybridization states and bonded or not to a hydrogen atom. The calculated NMR spectra show excellent agreement with experimental data and are thus useful to identify local structural features of disordered carbons.

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