We present density functional theory investigations of the bulk properties of cerium oxides (Ce O2 and Ce2 O3) and the three low index surfaces of Ce O2, namely, (100), (110), and (111). For the surfaces, we consider various terminations including surface defects. Using the approach of "ab initio atomistic thermodynamics," we find that the most stable surface structure considered is the stoichiometric (111) surface under "oxygen-rich" conditions, while for a more reducing environment, the same (111) surface, but with subsurface oxygen vacancies, is found to be the most stable one, and for a highly reducing environment, the (111) Ce-terminated surface becomes energetically favored. Interestingly, this latter surface exhibits a significant reconstruction in that it becomes oxygen terminated and the upper layers resemble the Ce2 O3 (0001) surface. This structure could represent a precursor to the phase transition of Ce O2 to Ce2 O3.
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