FORCE-FIELD PARAMETERIZATION OF COPPER(I)-OLEFIN SYSTEMS FROM DENSITY-FUNCTIONAL CALCULATIONS

A strategy for force field parameterization of relatively large transi tion metal systems to a reasonable cost using non-local density functi onal theory (DFT) has been developed. The strategy also makes it possi ble to derive parameters for dummy atoms, which often have to be used in transition metal systems in order for the force field to describe i nternal rotations correctly. The derived strategy has been used to dev elop force field parameters for a group of Cu(I)-olefin systems contai ning bisimino ligands. DFT was used to calculate energies for a set of distorted structures of a small model compound. The energies obtained were used for the derivation of the bonded parameter values within th e AMBER force field for the model compound by minimizing the sum of th e squared differences of relative DFT energies and relative MM energie s by a Monte Carlo random walk process. Partial charges were derived f rom electrostatic potential calculations. A value of the van der Waals radius for Cu(I) was also derived from DFT calculations. To validate the accuracy of the method, the DFT-computed structure of (ethylene)[d i-(2-pyridyl)amine]copper(I) was compared with that obtained from an X -ray crystallography study. Comparisons were also made between geometr ies and binding energies computed by the DFT approach and the MP2 meth od for the model compound. Normal mode analyses were performed with DF T and the AMBER force field, and a comparison of the frequencies and v ibrational modes compared confirm the validity of the parameters deriv ed. It was shown that the derived parameter set could be transferred t o some 5- and 6- membered ring systems. (C) 1997 Elsevier Science B.V.