DEPENDENCE OF THE SHIELDING TENSOR WITH A PROPOSED LOCAL GAUGE

A theoretical procedure for evaluating nuclear magnetic shielding and magnetic susceptibility tensors in molecules within a 'local gauge' tr ansformation is presented. The main features of our formulation are ce ntred on the fact that, even though the expressions resulting from the use of the Coulomb 'gauge' for the magnetic susceptibility tensor rem ain unchanged, it provides alternative expressions for the nuclear mag netic shielding tensor. This new result may be considered as an advant age because it allows a dependence of the nuclear magnetic shielding t ensor on the electric field and gradient held exerted by the electrons on the position of the nuclei to be shown in an explicit manner. Sum rules for charge and current conservation and 'gauge' invariance are a lso derived. Finally we mention that all these results are only valid for external uniform and time independent magnetic fields. (C) 1998 El sevier Science B.V. All rights reserved.