First-principles study of the composition, structure, and stability of the FeO (111) surface

We performed systematic full-potential density functional theory studies on all possible $(1\ifmmode\times\else\texttimes\fi{}1)$ terminations of the low-index surface (111) of FeO with NaCl $(B1)$ phase and inverse NiAs $(iB8)$ phase, respectively. Applying the concept of first-principles atomistic thermodynamics, we analyze the composition, structure, and stability of the FeO (111) orientation in equilibrium with an arbitrary oxygen environment. The density of states (DOS) of the relaxed FeO (111) surface with $B1$ structure and inverse $B8\phantom{\rule{0.3em}{0ex}}(iB8)$ structure within the studied subset of $(1\ifmmode\times\else\texttimes\fi{}1)$ geometries were calculated and compared with the DOS of the bulk FeO with the two structures. The calculations reveal that the (111) surfaces of $\mathrm{FeO}(B1)\text{\ensuremath{-}}\mathrm{Fe}$ and $\mathrm{FeO}(B1)\text{\ensuremath{-}}\mathrm{O}$ have metallic and ferromagnetic properties, and they are different from those of the bulk of FeO $(B1)$. While the (111) surfaces of $\mathrm{FeO}(iB8)\text{\ensuremath{-}}\mathrm{Fe}$ and $\mathrm{FeO}(iB8)\text{\ensuremath{-}}\mathrm{O}$ show semiconducting and antiferromagnetic properties similar to those of the bulk of $\mathrm{FeO}(iB8)$.