NUCLEAR-MAGNETIC-RESONANCE SPIN-SPIN COUPLING-CONSTANTS FROM DENSITY-FUNCTIONAL THEORY - PROBLEMS AND RESULTS

Our recently developed method for the calculation of indirect nuclear spin-spin coupling constants is studied in more detail. For the coupli ngs between nuclei other than N, O, and F (which have lone pairs) the method yields very reliable results. The results for (1)J(SI-H) coupli ngs are presented and their dependence on the basis set quality is ana lyzed. Also, (2)J(H-H) and (1)J(X-H) couplings (X=C, Si, Ge, Sn) in XH (4) molecules are presented and the relativistic effects on (1)J(X-H) are discussed. The limitations of the method, which is based on densit y functional theory, are connected with the inability of the present L DA and GGA exchange-correlation functional to describe properly the sp in-perturbations (through the Fermi-contact mechanism) on atoms to the right of the periodic table (containing lone pairs). However, the dev iations from experiment of the calculated couplings for such nuclei ar e systematic, at least for one-bond couplings, and therefore these cal culated couplings should still be useful for NMR structure determinati ons. (C) 1996 American Institute of Physics.