CHAPTER 12.4: Theoretical Calculations and NMR Spectroscopy

Quantum chemical calculations are most popular method to clarify the reasons for chemical phenomena and to evaluate many properties reliably. The theoretical background and the basic methods of the calculations are briefly explained for the chemical phenomena containing chalcogens from the viewpoint of the experimental chemist. DFT functionals, which have recently shown high performance, are discussed in some detail. Experimental chemists frequently employ the DFT functionals to understand and explain their experimental results, together with the higher levels. The relativistic effect seems necessary to predict properties, especially those for the higher elements. It is therefore surveyed here, exemplified by the zeroth‐order regular approximation (ZORA) level. Various calculations are discussed limiting the typical cases. Theoretical treatments of NMR parameters are also discussed, mainly on the basis of the theoretical background explained in this chapter. It is explained from the viewpoint of how the theoretical calculations can clarify the origin of the NMR parameters. The calculated results are closely related to the observed values, and are therefore crucially important in explaining the observed results. Applications of the methods are also discussed.