QM/MM Molecular Dynamics Simulation of the Structure of Hydrated Fe(II) and Fe(III) Ions

Abstract

The hydration shell structure of Fe(II) and Fe(III) ions in their high spin state has been studied by combined ab initio quantum mechanical/molecular mechanical (QM/MM) molecular dynamics simulations, in which the ion and its first hydration sphere were treated at the Hartree−Fock ab initio quantum mechanical level, whereas ab initio generated pair plus three-body potentials were employed for the remaining system. The coordination number in the first hydration shell is 6 for both Fe(II) and Fe(III) ions. The second hydration shell contains 12.4 and 13.4 water molecules for Fe(II) and Fe(III) ions, respectively, in good agreement with the experimental values. The residence time of a water molecule in the second hydration shells of Fe(II) and Fe(III) is 24 and 48 ps, respectively. The complex configuration and ligand orientations observed in this study prove that many-body effects play an important role in the hydration of both Fe(II) and Fe(III) ions. The hydration energies computed from the simulation are...