Thermodynamics of Iron Oxides and Oxyhydroxides in Different Environments

In recent years, computational modeling has opened up another potential way to solve the pending questions about the relative stability of different iron oxides and oxyhydroxides. Modeling of iron oxides and oxyhydroxides is challenging, due to the different magnetization states, the small energy differences between different states and solid phases, and the need for more advanced implementations to cope with the strong correlation effects and weak hydrogen bonds and van der Waals forces. Despite the difficulties, density functional theory (DFT) calculations have been successfully applied to some iron oxides and oxyhydroxides in recent years. In this chapter we will explore the relative stability of five iron oxides and oxyhydroxides, including magnetite, hematite, maghemite, goethite, and lepidocrocite, from the macro- to the nanoscale. In this context a general method for modeling the impact of size, shape, temperature, and chemical environment on the morphology and polymorphic stability (known as thermodynamic cartography) will also be described.