NUCLEAR-MAGNETIC-RESONANCE SHIELDING TENSORS CALCULATED WITH A SUM-OVER-STATES DENSITY-FUNCTIONAL PERTURBATION-THEORY

A sum-over-states perturbation theory is combined with density functio nal methodology (SOS-DFPT) and is applied to NMR shielding tenser calc ulations. Individual gauges for localized orbitals (IGLO) were used. D ifferent types of approximations for the energy difference of the grou nd and ''excited'' states are compared. The calculations were carried out using a modified version of the deMon program. The results of NMR shielding tenser calculations using SOS-DFPT are in good agreement wit h those of the best post-Hartree-Fock approaches and also with experim ental data. Results are presented for a number of organic and inorgani c compounds (including transition metal complexes) and for a model dip eptide.