Importance of charge transfer and polarization effects for the modeling ofuranyl-cation complexes

The structures, energies, and charges of uranyl cation complexes with water molecules, nitrate ion, and carbonate ions were determined using Hartree-F ock, second-order Moller-Plesset (MP2) perturbation theory, and density fun ctional theory (DFT) ab initio quantum chemical methods. Reasonable agreeme nt with experimentally determined structures was found. Significant polariz ation of the ligands as well as charge transfer to the uranyl ion was obser ved in the complexes; The dissociation energy curves for the complexes were also determined at the MP2 level of theory. Attempts to reproduce these cu rves with molecular mechanical models with fixed atomic point charges faile d, showing that an appropriate force field for these systems must include p olarization and charge-transfer effects.