A force field for molecular dynamics simulations of iron oxide system

Iron oxide nanomaterials have been widely utilized in the field of healthcare, but the understanding on the synthetic mechanism of crystal nanoparticles is insufficient. Molecular dynamics (MD) simulation provides a numerical method to investigate the structural transformation from free ions to ordered crystal. However, the definition of proper force field parameters is a vital challenge for iron oxide system. In this study, we fitted the parameters of Coulombic-Buckingham potential based on multiple initial parameters via considering force balance of ions in crystal structures. Our fitted force field was validated according to lattice constants and elastic properties obtained from previously published experiments. The long-range ordered FeO crystal structure was reproduced by gradually aggregating ions in MD simulations adopting the force field. With the enhancement of relaxing temperatures from 600 K to 1500 K, β-Fe₂O₃ crystal phase were transformed from amorphous or short-range ordered structures like ε-Fe₂O₃, in good agreement with published experimental results.