A MOLECULAR-DYNAMICS STUDY OF THE CR3+ HYDRATION BASED ON A FULLY FLEXIBLE HYDRATED ION MODEL

A theoretical study of the Cr3+ hydration in aqueous solutions has bee n carried out by means of molecular dynamics (MD) simulations. Ion-wat er intermolecular interaction potentials are based on first principles using the idea of the previously developed hydrated ion-water interac tion potential: The bare ion, Mn+, is replaced by its corresponding hy drate, [M(H2O)(6)](n+), and the water molecules interact with the hydr ate by means of an ab initio [M(H2O)(6)](n+)-H2O interaction potential . new ab initio interaction potential has; been developed to describe the Mn+ - (H2O)(first-shell) interaction based on an examination of th e hexahydrate potential-energy surface section that distorts the posit ion of one of the cluster water molecules, the remaining five fixed at their equilibrium position. These two complementary interaction poten tials, which describe ion-water interactions have been combined with t he TIP4P model for water molecules. Structural and dynamical results d erived 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 c luster are examined by comparing the present results with those previo usly obtained with a model of rigid hexahydrate [J. Phys. Chem. B 102, 3272 (1998)]. A new definition of hydrated ion based on the rotationa l properties of its hydrate is supported. (C) 1998 American Institute of Physics.