NMR computations for carbon nanotubes from first principles: Present status and future directions

Abstract

NMR (nuclear magnetic resonance) is a versatile experimental tool to study the properties of molecules and solids. It has been proposed that reliable computational data of the 13 C NMR chemical shifts of different types of carbon nanotubes may be used to guide experimental characterization by NMR. Within the last few years this field has become quite active. After outlining the background for first-principles calculations, as well as early model calculations, we focus on recent first-principles theoretical studies performed toward this end. Studies on finite and infinite SWNT systems have indicated that 13 C NMR may be used to determine the diameter distribution of the tubes in a bulk sample. The Knight shift of metallic tubes has been examined. NICS (nucleus independent chemical shifts) have yielded information about the aromaticity of various systems, and the NMR chemical shifts of small molecules trapped in nanotubes have been calculated. Work on SWNTs functionalized with NR groups has suggested that 13 C NMR may be used to determine which nanotube carbons are derivatized, and perhaps even yield information about the diameter of the tubes. It has also been found that 13 C NMR may be useful to quantify the degree of fluorination. Studies on Stone-Wales defects have indicated that well-resolved NMR signals may arise from atoms in the defect site. Shielding tensor data is also discussed. The theoretical progress made in this field shows that a wealth of information is contained within the NMR chemical shifts of carbon nanotubes.

DFT calculation of structures and NMR chemical shifts of simple models of small diameter zigzag single wall carbon nanotubes (SWCNTs)

“…[33 -36] Recently, a detailed review on calculations of NMR properties of CNTs was published. [37] Indeed, some theoretical calculations pointed out the possible dependence of chemical shifts with the SWCNT diameter. [30] However, the recent solidstate NMR measurements of metallic and semiconducting 13 C enriched SWCNT distinguished only single carbon signal of very similar chemical shift at about 122 and 123 ppm, respectively.…”

Applications of nuclear shielding

“…NICS (nucleus independent chemical shifts) yielded information about the aromaticity of various systems, and the NMR chemical shifts of small molecules trapped in nanotubes were calculated. 235 Nuclear shieldings, including the Fermi contact and pseudocontact terms, were calculated with DFT methods in a variety of open-shell molecules (nitroxides, aryloxyl and various transition-metal complexes), thereby predicting 1 H and 13 C chemical shifts. When experimental data were reliable a good agreement with experimental values was observed, thus demonstrating the predictive power of DFT also in this context.…”

Calculation of Raman parameters of real-size zigzag (n, 0) single-walled carbon nanotubes using finite-size models

“…In particular, many DFT based studies on structural parameters, energetics or spectral properties (mainly NMR) of SWCNTs have been reported. 36,[68][69][70][71][72][73][74] Despite the fact that the Raman scattering is one of the most common methods investigating SWCNTs experimentally, theoretical studies on Raman characteristics of nanotubes using the first-principles methods are still rather rare. Popov et al using the tight binding approach studied Raman features of pristine nanotubes.…”