A molecular dynamics study of the Cr3+ hydration based on a fully flexible hydrated ion model

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Abstract
A theoretical study of the Cr3+ hydration in aqueous solutions has been carried out by means of molecular dynamics (MD) simulations. Ion–water intermolecular interaction potentials are based on first principles using the idea of the previously developed hydrated ion–water interaction potential: The bare ion, Mn+, is replaced by its corresponding hydrate, [M(H2O)6]n+, and the water molecules interact with the hydrate by means of an ab initio [M(H2O)6]n+–H2O interaction potential. A new ab initio interaction potential has been developed to describe the Mn+–(H2O)first-shell interaction based on an examination of the hexahydrate potential-energy surface section that distorts the position of one of the cluster water molecules, the remaining five fixed at their equilibrium position. These two complementary interaction potentials, which describe ion–water interactions have been combined with the TIP4P model for water molecules. Structural and dynamical results derived from the analysis of 1 ns of simulation for a sample formed by [Cr(H2O)6]3+ and 512 H2O are presented. Rigidity effects of the cluster are examined by comparing the present results with those previously obtained with a model of rigid hexahydrate [J. Phys. Chem. B 102, 3272 (1998)]. A new definition of hydrated ion based on the rotational properties of its hydrate is supported.

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