Nucleation and Coalescence of Wüstite-like Motifs in Oxygen-Deficient Magnetite: A Deep-Potential Molecular Dynamics Study

Abstract

Oxygen loss in magnetite drives the cation redistribution and local structural reconstruction that control the rate of iron oxide reduction, but this coupling has resisted direct simulation: the reconstruction develops far beyond DFT-accessible scales, and classical potentials cannot describe mixed-valence Fe–O with the required fidelity. We developed a DFT-validated Fe–O Deep Potential trained on bulk, defective, and surface configurations and applied it in large-scale molecular dynamics with an imposed stochastic oxygen-removal protocol. The potential reproduces DFT energy and force trends together with vacancy and surface energetics. DFT single-point checks on oxygen-deficient configurations and equation-of-state calculations for Fe₃O₄ and FeO further delineate the transferability of the potential, with larger deviations emerging in the most strongly oxygen-deficient states. As oxygen is removed, four-coordinated O environments decrease while six-coordinated wüstite-like motifs emerge, grow, and coalesce into extended local domains. Deep-Potential nudged elastic band (DP-NEB) calculations, benchmarked against selected DFT single-point energies, show that the coupled O/Fe-vacancy configuration gives the lowest Fe-migration barrier among the selected local rearrangement pathways. Time-windowed mean-squared displacements yield apparent Fe and O diffusivities that evolve in the nonstationary lattice. These simulations establish a defect-mediated solid-state response toward wüstite-like local order under imposed oxygen-deficient conditions, rather than the formation of a complete equilibrium Fe_1–xO phase. The protocol isolates oxide-side reconstruction and does not explicitly treat hydrogen chemistry.