Ab Initio Molecular Dynamics Study of the Electronic Structure of Superoxide Radical Anion in Solution

Ab intitio molecular dynamics simulation of the electronic structure of the aqueous superoxide anion (O-2(-)) has been carried out using the Car-Parrinello density functional theory at 298 and 310 K. The modeling system consists of one O-2(-) solvated in 31 water molecules. On the basis of our 40 ps production run, the novel mechanism and the nature of the hydration of the superoxide anion in a relatively big aqueous environment have been revealed by using various radial distribution functions. The averaged coordinated water number was estimated to be 4.5. The calculated microscopic configurations of the first solvation shell are in good agreement with the experimental results. The vibrational frequency of the solvated O-2(-) anion was red-shifted significantly in comparison with that of the free radical anion in the gas phase. The diffusion coefficient of O-2(-) was estimated to be about 8 x 10(-5) cm(2)/s at 298 K. Comparisons with the previous force-field-based classical molecular dynamics simulations have been made, and the differences were discussed.