Predictive Quantum Mechanics-Based Force Field for Iron Oxide Systems: Mechanical, Dielectric, and Piezoelectric Response in Hematite, Magnetite, Maghemite, and Wüstite

Iron oxide systems are well-known for their diverse magnetic and electronic properties, making them pivotal in materials science, catalysis, and biomedical applications. Among these, Fe3O4 (magnetite) stands out as a ferrimagnetic half-metallic material with exceptional versatility. Through controlled oxidation or reduction, Fe3O4 can transform into other iron oxide phases, such as wüstite (Fe1–xO), an antiferromagnetic phase, or γ-Fe2O3 and α-Fe2O3, which exhibit ferrimagnetic and antiferromagnetic insulating behaviors, respectively. These phase transitions provide a unique platform for tuning the magnetic and electrical properties of iron oxides. In this work, we present the development of a novel force field (FF′) specifically designed to model the structural, mechanical, dielectric, and piezoelectric properties of iron oxide systems. By capturing the intrinsic relationships between Fe3O4 and its oxidized and reduced counterparts, this force field provides a unified framework for simulating phase transitions and property tuning in iron oxides. The force field is parametrized based on the quantum-mechanical structure of Fe3O4 and extended to accurately describe the properties of γ-Fe2O3, α-Fe2O3, and Fe1–xO. Our FF′ successfully reproduced quantum mechanical calculations for the elastic constants, dielectric responses, and piezoelectric coefficients across these phases. This study highlights the potential of FF′ as a robust tool for molecular dynamics simulations of iron oxide systems across diverse compositions and applications. The ability to accurately model phase-dependent magnetic and electric properties makes this force field particularly valuable for advancing the design of magnetoelectric devices, catalysts, sensors, and biomedical materials.