Structure-breaking effects of solvated Rb(I) in dilute aqueous solution--an ab initio QM/MM MD approach

Structural properties of the hydrated Rb(I) ion have been investigated by ab initio quantum mechanical/molecular mechanical (QM/MM) molecular dynamics (MD) simulations at the double-zeta HF quantum mechanical level. The first shell coordination number was found to be 7.1, and several other structural parameters such as angular distribution functions, radial distribution functions and tilt- and theta-angle distributions allowed the full characterization of the hydration structure of the Rb(I) ion in dilute aqueous solution. Velocity autocorrelation functions were used to calculate librational and vibrational motions, ion-ligand motions, as well as reorientation times. Different dynamical parameters such as water reorientation, mean ligand residence time, the number of ligand exchange processes, and rate constants were also analyzed. The mean ligand residence time for the first shell was determined as tau = 2.0 ps.