The reduction of FeO (wüstite) to Fe represents the final and slowest step in the hydrogen-based direct reduction of iron ores for sustainable ironmaking. However, the atomistic-scale mechanisms and kinetics of this process remain poorly understood. Here, we employ ab initio meta-dynamics simulations to investigate reaction pathways and energy barriers for this redox process on FeO(1 0 0) and FeO(1 1 1)_O-terminated surfaces. Differences in surface configurations lead to variations in the number of H₂ molecules required, reaction pathways, and energy barriers. The FeO surface exhibits an autocatalytic effect, facilitating H₂ dissociation and reducing the energy barrier for breaking H₂ molecular bonds. Nevertheless, hydrogen dissociation and adsorption, forming O–H bonds, constitute the primary rate-limiting step. Following this, the Fe-O bond spontaneously breaks in the presence of individual H atoms. Increasing H₂ partial pressure enhances reaction efficiency by raising the density of reactive H₂ molecules, consistent with macroscopic observations. These insights advance the atomistic-scale understanding of hydrogen-based direct reduction, highlighting the influence of pressure and rate-limiting factors.

With the aim to find the best simulation routine to accurately predict the ground−state structures and properties of iron oxides (hematite, magnetite, and wustite) using density functional theory (DFT) with Hubbard-U correction, a significant amount of DFT calculations were conducted to investigate the influence of various simulation parameters (energy cutoff, K-point, U value, magnetization setting, smearing value, etc.) and pseudopotentials on the structures and properties of iron oxides. With optimized simulation parameters, the obtained equation of state, lattice constant, bulk moduli, and band gap is much closer to the experimental values compared with previous studies. Due to the strong coupling between the 2p orbital of O and the 3d orbital of Fe, it was found that Hubbard-U correction obviously improved the results for all three kinds of iron oxides including magnetite which has not yet been tested with U correction before, but the U value should be different for different oxides (3 ev, 4 ev, 4 ev for hematite, magnetite, and wustite, respectively). Two kinds of spin magnetism settings for FeO are considered, which should be chosen according to different calculation purposes. The detailed relationship between the parameter settings and the atomic structures and properties were analyzed, and the general principles for future DFT calculation of iron oxides were provided.