Simulating iron in oxygen-containing environments: An improved Fe–O interaction for density-functional tight-binding

Abstract

The chemistry of iron in oxygen-containing and wet environments plays a central role in corrosion, (electro)catalytic reactions, and several biological processes. These processes hinge on the molecular-level interactions between iron and various oxygen-containing species such as water, molecular oxygen, oxygen radicals, and functional groups such as alcohols or carboxyls. Although the first-principles density-functional theory (DFT) describes these interactions well, DFT is often too slow to simulate the thermodynamics and kinetics of the above-mentioned processes at the necessary time and length scales. Fortunately, second-principles density-functional tight-binding (DFTB) satisfies these traits once properly parameterized for the target systems. Here, we discuss the problems that current DFTB parameterizations have with Fe–O pairwise repulsion, a central contributor to the DFTB performance. We construct an improved Fe–O repulsion by fitting the repulsion to structures relevant for topical research and benchmark it against structures with free and adsorbed Fe interacting with water and other oxygen-containing species. We explore the improved interaction by simulating the dynamics of atomic Fe and FeN4-modified graphene in aqueous environments, demonstrating the applicability of the parameterization to catalytically relevant large-scale simulations.