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A Density Functional Study of O2 Adsorption on (100) Surface of gamma-Uranium

We have studied the chemisorption processes of O2 on the (100) surface of uranium using generalized gradient approximation to density functional theory. Dissociative adsorptions of O2 are significantly favored compared to molecular adsorptions. We found interstitial adsorption of molecular oxygen to be less probable, as no bound states were found in this case. Upon oxygen adsorption, O 2p orbitals is found to hybridize with U 5f bands, and part of the U 5f electrons become more localized. Also there is a significant charge transfer from the first layer of the uranium surface to the oxygen atoms, which made the bonding partly ionic. For the most favored site the dissociative chemisorption energy is approximately 9.5 eV, which indicates a strong reaction of uranium surface with oxygen. Spin polarization does not have a considerable effect on the chemisorption process. For most of the sites and approaches, chemisorption configurations are almost same at both spin-polarized and non-spin-polarized cases. For the most favored chemisorption sites of oxygen on uranium, paramagnetic adsorption is slightly stronger, by 0.304 eV, than the magnetic adsorption.