Water dissociation on the reduced PuO2(110) surface from first principles

We present a first-principles investigation on the dynamics and mechanism of the oxidation reaction between water molecules and the reduced PuO2(110) surface using ab initio molecular dynamics (AIMD) simulations in combination with density functional theory (DFT) + U calculations. We find a dominating dissociation preference of water molecules for the vacancy defect sites on the PuO2(110) surface, irrespective of the water or vacancy coverage. Due to hybridizations between the frontier orbitals of water molecule and the electronic states of the vacancy vicinity, partial water dissociation at the vacancy sites is exothermic and barrierless. The dissociation product, an OH group, further hydrogenates the PuO2(110) surface by occupying the vacancy site. We also observe surface vacancy diffusion induced by the interactions between the water molecules and the surface oxygen atom in the proximity of the defect sites.