Surfaces of magentite (Fe3O4) are of widespread interest due to their geochemical and catalytic reactivity. As with many transition metal oxides, the stoichiometry and structure of Fe3O4 surfaces are sensitive to temperature and pressure conditions of oxygen and water. Additionally, Fe3O4 is a strongly correlated material, which poses additional challenges to accurate modeling through density functional theory (DFT) methods. In this study, we investigate the (111) surfaces of Fe3O4, the most common growth face, using DFT and ab initio thermodynamics. In particular, we aim to provide a thermodynamic explanation for differences between structures determined by experiments carried out under ultra-high vacuum conditions and ambient conditions with finite water pressures. Unique to our approach is the application of specific Hubbard U values for each unique Fe atom in the surface. We provide a detailed analysis of how this DFT + U(Fe) treatment affects the electronic structure of the surface, the Fe-O bonding in the mineral, and the surface free energies.

Theoretical phase diagram for Fe3O4 (111) surfaces using a DFT + U(Fe) approach

249th National Meeting (2015)

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