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

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 ¹³C 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 ¹³C 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 ¹³C 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 ¹³C 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.