Ab Initio Calculations of NMR Chemical Shielding

Abstract

Publisher Summary This chapter gives an overview of the current state of ab initio calculations of the NMR chemical shielding. It provides a general overview citing some of the limitations and problems one faces in carrying out the chemical shielding calculations and quantum mechanical calculations in general. Then the basics of the theory are presented in the chapter. Many of the calculations of chemical shielding discussed are done at the Hartree-Fock level on rigid and isolated molecules. The main approaches to the calculations are examined (mainly, the various ways of combating the gauge problem), and then are presented that are representative illustrations of shielding calculations, beginning at the Hartree-Fock level and ending with the more recent attempts to include electron correlation. Chemical shielding is a tensor quantity and is generally described in terms of the three principal values of the symmetrized shift tensor and the orientation of its principal axes. The chapter discusses some examples, including correlation in shielding the calculations by way of many body of MOller-Plesseth perturbation theory in the GIAO method, the implementation of the second-order polarization propagator (SOPPA) method that incorporates the localized-orbital-local-origin (LORG) methodology called SOLO (second-order LORG), a non-perturbative multi-configuration extension of IGLO called MC-IGL, and finally an example employing the density function theory.