Hydration of Cd(II): molecular dynamics study

An ab initio two-body potential and a function correcting for 3-body effects for Cd(II)-water system are constructed. The hydration structure of Cd(II) has been studied by means of molecular dynamics simulations. The inclusion of the three-body correction was found to be crucial for the description of the system, and results thus obtained are in good agreement with experimental values. Radial distribution functions, coordination number distributions, and various angular distributions have been used to discuss details of the hydration structure, together with bond lengths and bond angles of the water molecules in the first hydration shell. The Cd(II) is found 6-fold coordinated. Water molecules in the first hydration shell are shown to be polarized compared to the gas-phase structures. Umbrella-sampling molecular dynamics simulations were performed to investigate the water exchange reaction of Cd(II) ion in aqueous solution. The water-exchange rate constant at 298 K is estimated by the transition state theory to be 4.9 x 108 s-1, assuming a transmission coefficient of unity.