The average structures, hydration free energies and dynamic behavior of aqueous trivalent actinide (An) ions (An=U, Np and Pu) have been examined using polarizable (AMOEBA) and non-polarizable (SPC and TIP3P) force fields in molecular dynamics simulations. Various An-OH2 interaction potentials are developed using ForceFit program. The potentials have been generated on the basis of fitting to the ab initio gradients of the H2O dissociation potential energy surface (PES) of [An-(H2O)]3+, [An-(H2O)8]3+ and [An-(H2O) 9]3+ species. Molecular dynamics simulations of An3+ solvation in bulk water have been subsequently performed with all the three water models using the best-fitted potentials. While both polarizable and non-polarizable potentials can reproduce average hydration numbers very well compared to experiment, the dynamic features are incredibly dependent upon the specific force field implemented. Further, only the force fields that are fitted within a polarizable framework are able to accurately determine the free energy of solvation of these trivalent ions when using the Bennett acceptance ratio (BAR) method. This work thus highlights that much care needs to be taken when developing force fields for actinides and that average structural parameters are not necessarily good metrics of force field quality.

Solvation thermodynamics of trivalent actinide (An=U, Np and Pu) ions using polarizable force field

249th National Meeting (2015)

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