Book Description

The theory and quantum-chemical calculations of the spectral parameters of nuclear magnetic resonance (NMR) are well established in the case of diamagnetic, closed-shell molecules. In contrast, NMR calculations of paramagnetic, open-shell molecules (pNMR) are scarce, limited by both assumptions within the underlying theoretical background as well as the availability of computational implementations. We discuss the systematic development of pNMR theory that recently culminated in a novel, general and systematic electronic structure approach for the shielding tensor and the associated chemical shift for paramagnetic, open-shell atoms, molecules, and nonmetallic solids. The approach has now been extended for the first time to a higher than doublet spin state as well as arbitrary spatial symmetry. The approach is formulated without reference to spin susceptibility, in contrast to the contemporary experimental procedure and approximate quantum-chemical treatment of axial zero-field splitting. As a result of the systematic procedure, all the temperature-dependent hyperfine shielding terms are generalized and, for example, the leading-order nonrelativistic dipolar term now provides an isotropic chemical shift contribution for species with triplet and higher spin multiplicity. Recent first-principles quantum-chemical calculations of pNMR chemical shifts are reviewed both using the novel theory as well as earlier approaches.