The Magnetite (001) Surface: Insights from Molecular Dynamics Calculations
A classical polarizable potential model is used in a molecular dynamics model of the magnetite (001) surface. The model, previously applied to the tetrahedral, or “A” termination of magnetite (001) is here applied to the octahedral or “B” termination, as well as to the hydroxylation of both the “A” and “B” termination. Surface relaxations for the “B” terminated surface are small, and consistent with the observed (√2×√2)R45 cell observed in LEED experiments. Additionally, it is shown that the relaxation of a tetrahedral defect on the “B” terminated surface does not give rise to the same relaxation mechanism as that calculated for the tetrahedral sites on the “A” surface. The lack of a “dimer” forming at the defect site is consistent with recent STM studies. Calculations on charge-ordered magnetite slabs indicate that, within the context of the ionic model used here, the surface energy of the “A” termination of magnetite is lower than that of the “B” termination over a wide range of oxygen ftigacities. Hydr xylation has a negligible effect on the relative energies of the “A” and “B” surfaces, however, the large gain in energy associated with tetrahedral ion relaxation on the “A” surface could explain the lack of two high temperature peaks expected for successive removal of adsorbing waters from the same tetrahedral site.
KeywordsOctahedral Site Oxygen Fugacity Tetrahedral Site Ferric Oxide Ionic Model
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