An Ab Initio Molecular Dynamics Study on the Hydrolysis of the Po(IV) Aquaion in Water

Po(IV) in water has been studied by means of Car-Parrinello molecular dynamics (CPMD) simulations. A new Trouiller Martins pseudopotential for Po(I V) has been developed. This pseudopotential was tested by comparing the structure and energetics of small [Po(H2O)(n)(OH)(m)](4-m) clusters optimized quantum-mechanically. CP-MD simulations of 1 Po + 60 H2O were carried out starting from three different degrees of hydrolysis of the aquaion (m = 0, 2, and 3), in order to check the stability of the hydrolyzed forms under the simulation conditions. The three simulations converge to a description of the solution where the same hydrolyzed species are present. Dynamics of the octahydrate aquaion in water indicates that dehydration couples to hydrolysis processes, and the total coordination number decreases with the hydrolysis degree. The time evolution of the initial [Po(H2O)(8)](4+) aquaion in aqueous solution indicates that hydrolysis precedes to dehydration in the process from aquaion to hydroxoaquaion. Structural and dynamical properties of the ligands in the first coordination shell are analyzed. The power spectra and its contribution from fragments of the first coordination shell are also examined.