Effect of rotation and vibration on nuclear magnetic resonance chemical shifts: Density functional theory calculations

The effect of rotation and vibration on the nuclear magnetic resonance (NMR ) shielding constants was computed for HF, F-2, N-2, CO, and HBr. The shiel ding constants for H, C, N, O, and F nuclei were calculated using sum-over- states density functional perturbation theory (SOS-DFPT). Diatomic ro-vibra tional states were calculated from a discrete variable representation using Morse potentials and potential curves calculated with density functional t heory. Our ro-vibrational corrections to shielding constants for HF, CO, F- 2, and N-2 molecules are in good agreement with experimental data and CCSD( T) calculations. These results together with satisfactory first and second derivatives of the shielding constants with respect to interatomic distance s confirm that the shielding surfaces produced by the SOS-DFPT method are o f good accuracy, providing reassurance of the use of these methods for more complex systems. The unusual temperature dependence of the hydrogen chemic al shift in HBr and a first attempt to include both relativistic spin-orbit and ro-vibration effects are discussed. (C) 1999 American Institute of Phy sics. [S0021-9606(99)30314-7].