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