Ab Initio Extension of the AMOEBA Polarizable Force Field to Fe2+

Abstract : We extend the AMOEBA polarizable molecular mechanics force field to the Fe2+ cation in its singlet, triplet, and quintet spin states. Required parameters are obtained either directly from first principles calculations or optimized so as to reproduce corresponding interaction energy components in a hexaaquo environment derived from quantum mechanical energy decomposition analyses. We assess the importance of the damping of point-dipole polarization at short distance as well as the influence of charge-transfer for metal-water interactions in hydrated Fe2+; this analysis informs the selection of model systems employed for parametrization. We validate our final Fe2+ model through comparison of molecular dynamics (MD) simulations to available experimental data for aqueous ferrous ion in its quintet electronic ground state.