Assessment of density functional methods for nuclear magnetic resonance shielding calculations

Several different methods for calculating nuclear magnetic resonance shieldings in density functional theory are compared. All methods were implemented using gauge-including atomic orbitals to eliminate gauge dependence. The calculated shielding tensors are compared to accurate coupled cluster results with perturbative triples correction and to experimental data. We have implemented a simple method based on a uniform shift of virtual orbital energies and determined the optimum level shift in small molecules. Of the methods tested, the uniform level shift and procedure of Wilson, Amos, and Handy show the best performance. Malkin's correction also gave good results. The optimized exchange functional of Cohen and Handy, in conjunction with the Lee-Yang-Parr (LYP) correlation functional, gives a marked improvement over the Becke exchange plus LYP. (C) 2003 American Institute of Physics.