Ab-Initio Calculation and Analysis of Nuclear Magnetic Shielding Tensors: the LORG and SOLO Approaches

Abstract

The localized orbital/local origin approach labelled LORG to first order and SOLO to second order in electron correlation is reviewed in the general context of ab-initio calculations of nuclear shielding tensors. The performance is illustrated and discussed for a range of molecules containing 13 C 15 N and 19F nuclei. We discuss tensorial aspects of nuclear shielding emphasizing the shielding antisymmetry for nuclei at sites of low symmetry, and show how a decomposition of the paramagnetic contributions to the shielding tensor elements into symmetry species can assist the identification of electronic structures reponsible for antisymmetry. For first row nuclei the trend in the effects of second order electron correlation is towards increased isotropic shieldings and decreased anisotropies, generally improving agreements with experiments significantly.