SUM-OVER-STATES DENSITY-FUNCTIONAL PERTURBATION-THEORY - PREDICTION OF RELIABLE C-13, N-15, AND O-17 NUCLEAR-MAGNETIC-RESONANCE CHEMICAL-SHIFTS

Sum-over-states density functional perturbation theory (SOS-DFPT) has been used to calculate C-13, N-15, and O-17 NMR chemical shifts of 20 molecules, for which accurate experimental gas-phase values are availa ble. Compared to Hartree-Fock (HF), SOS-DFPT leads to improved chemica l shift values and approaches the degree of accuracy obtained with sec ond order Moller-Plesset perturbation theory (MP2). This is particular ly true in the case of N-15 chemical shifts where SOS-DFPT performs ev en better than MP2. Additional improvements of SOS-DFPT chemical shift s can be obtained by empirically correcting diamagnetic and paramagnet ic contributions to compensate for deficiencies which are typical of D FT. (C) 1996 American Institute of Physics.