Modeling charge redistribution at magnetite interfaces in empirical force fields

Magnetite shows enormous potential from biocompatible hybrid materials to heterogeneous catalysis. However, a detailed atomistic understanding of magnetite in complex nanostructures and at interfaces is required to unfold these potentials. Methods capable of treating (several) thousands of atoms and achieving an optimal balance between accuracy and efficiency are therefore in great demand. Here, a new empirical force field for the (001) and (111) magnetite surfaces is developed using partial point charges derived from ab initio Bader charge analyses. An accurate description of electrostatic interactions enables the modeling of magnetite-organic and magnetite-water interfaces. Consequently, surface charge redistribution is proposed as the most relevant mechanism for the surface reconstruction of magnetite and the bidentate binding of ligands. The produced force field results are in excellent agreement with the latest findings on magnetite. The approach can be further applied to magnetite nanoparticles and easily extended to oxide and other ionic crystal surfaces.