Density Functional Calculations of NMR Spin-Spin Coupling Constants for Heavy Atom Systems J. Autschbach and T. Ziegler Department of Chemistry, University of Calgary, Calgary,Alberta, Canada T2N 1N4   The development of efficient ways to predict properties such as NMR parameters of systems containing heavy elements is one of the major goals of contemporary quantum chemistry. During the last decade, it has been demonstrated that NMR spin-spin coupling constants are computationally accessible by means of nonrelativistic functional theory for a largevariety of molecules containing 1st to 3rd row main group as well as 3d transition metal elements. However, for couplings involving heavy nuclei like 183W, 195Pt, 199Hg or 207Pb, a  relativistic approach is absolutely necessary due to the dramatically large relativistic effects on the coupling constants, which depend on features of the wavefunction very close to the nuclei. We present a density functional formalism for the efficient computation of NMR spin-spin coupling constants based on the ZORA relativistic method. The most important terms arising in this formalism were implemented into the ADF density functional program and applied to 6th row main group and 5d transition metal systems. The results are very promising, but also indicate that for some systems higher orders might be important.