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revised on 22.02.2019 and posted on 22.02.2019by James Pegg, Ashley E. Shields, Mark T. Storr, David Scanlon, Nora De Leeuw
The interaction of atomic and molecular hydrogen with the
actinide dioxide (AnO2, An = U, Np, Pu) (111) surfaces has been
investigated by DFT+U, where noncollinear 3k antiferromagnetic (AFM) behaviour
and spin-orbit interactions (SOI) are considered. The adsorption of atomic
hydrogen forms a hydroxide group, and is coupled to the reduction of an
actinide ion. The energy of atomic hydrogen
adsorption on the UO2 (0.82 eV), NpO2 (-0.10 eV), and PuO2
(-1.25 eV) surfaces has been calculated. The dissociation of molecular hydrogen
is not observed, and shown to be due to kinetic rather than thermodynamic
factors. As a barrier in the formation of a second hydroxyl group, an unusual charge
distribution has been shown. This is possibly a limitation of a (1·1) unit cell
method. The recombination of hydrogen ions on the AnO2 (111)
surfaces is favoured over hydroxide formation.