Stability and speciation of hydrated magnetite {111} surfaces from ab initio simulations with relevance for geochemical redox processes

Magnetite is a common mixed Fe(II,III) iron oxide in mineral deposits and the product of (anaerobic) iron corrosion. In various Earth systems, magnetite surfaces
participate in surface mediated redox reactions. The reactivity and redox properties of the magnetite surface depend on the surface speciation, which varies with the environmental conditions. In this study, Kohn-Sham density functional theory (DFT+U method) was used to examine the stability and speciation of the magnetite crystal face
{111} in a wide range of pH and Eh conditions. The simulations reveal that oxidation state and speciation of the surface depend strongly on imposed redox conditions and,
in general, differ from those of the bulk state. Corresponding predominance phase diagrams for the surface speciation and structure were calculated from first principles.
1The obtained knowledge of surface structure and oxidation state of iron is essential for modeling retention of redox-sensitive nuclides. Further, classical molecular dynamics
(MD) simulations were conducted investigating the mobility of water near the magnetite surface.