Molecular dynamics simulation of iron(III) and its hydrolysis products in aqueous solution

A simple potential model is described which allows molecular dynamics simulations to be performed for ferric iron ions in dissociating aqueous solutions. The model was parametrized by fitting the polarizable dissociating water model of Halley et al [J. Chem. Phys. 98, 4110 (1993)] to a single water molecule-ferric iron ion potential energy surface taken from the work of Curtiss et al [J. Chem. Phys. 86, 2319 (1987)]. The model gives very good results forthe structure of the solvated hexaaqua iron(III) complex; the proper coordination number of 6 was obtained when the Fe-O interaction was fit directly to the ab initio calculations without further modification. The model produces adequate results for the first hydrolysis constant, but breaks down for the second hydrolysis constant, which is overestimated by 18 kcal/mol.