First-principles ion-water interaction potentials for highly charged monatomic cations. Computer simulations of Al3+, Mg2+, and Be2+ in water

The concept of hydrated ion [M(H2O)(m)](n+) has been used to describe inter actions of highly charged monatomic cations in water. Ab initio interaction potentials for Al3+, Mg2+ and Be2+ have been developed on the basis of tha t previously applied to the Cr3+ hydration study (Martinez et al. J. Chem. Phys. 1998, 109, 1445). Transferability of the different contributions to t he intermolecular potentials that describe the interactions between the cen tral cation and the first hydration shell, Mn+-(H2O)(I), and the hydrate wi th bulk water molecules, [M(H2O)(m)](n+)-(H2O)(bulk), have been examined. R esults indicate that a reduced number of points (similar to 40 quantum chem ical computations) are enough to get the basic and differential features of each cation. MD simulations (200 ps) for the hydrate of each cation plus 5 12 TIP4P H2O have been performed. Structural properties such as RDFs among different pairs of atoms in the system and orientational parameter are pres ented. Likewise, dynamical properties such as self-diffusion coefficients, reorientational and mean residence times, and power spectra have been obtai ned and analyzed. The comparative study of the properties derived from the hydration of each cation and the degree of transferability of the intermole cular potentials based on their main features is thoroughly discussed. Pros pectives and benefits introduced by this type of flexible hydrated ion-wate r interaction potential in molecular simulations are pointed out.