Structure and motifs of iron oxides from 1 to 3 TPa

Iron oxides are fundamental components of planet-forming materials.\nUnderstanding the Fe-O system's behavior and properties under high pressure can\nhelp us identify many new phases and states possible in exoplanetary interiors,\nespecially terrestrial ones. Using the adaptive genetic algorithm (AGA), we\ninvestigate the structure of iron oxides for a wide range of stoichiometries\n($0.25\\leq x_O \\leq 0.8$) at 1, 2, and 3 TPa. Five unreported ground-state\nstructures with Fe$_2$O, FeO, Fe$_3$O$_5$, FeO$_2$, and FeO$_4$ compositions\nare identified. The calculated density of states (DOS) suggests that, except\nfor FeO$_4$, all phases are metallic, but their carrier densities decrease with\nincreasing pressure and oxygen content. The cluster alignment analysis of\nstable and metastable phases shows that several motifs may co-exist in a\nstructure of iron oxides with low O content. In contrast, most iron oxides with\nhigh O content adopt a simple BCC motif at TPa pressures. Our results provide a\ncrystal structure database of iron oxides for modeling and understanding the\ninteriors of exoplanets.\n