First-principles study of the polar (111) surface of Fe3O4

We performed a systematic full-potential density functional theory study with the generalized gradient and local density approximation+U approaches on five possible (1x1) terminations of the low-index polar (111) surface of Fe3O4. Applying the concepts of first-principles thermodynamics, we analyze the composition, the structure, and the stability of the Fe3O4 (111) orientation at equilibrium with an arbitrary oxygen environment. The densities of states of the unrelaxed and relaxed Fe3O4 (111) surfaces were calculated and compared with that of bulk Fe3O4. The calculations reveal that the Fe-oct2-Fe-tet1-O1-terminated surface is energetically favored, showing metallic properties. The Fe-oct1-O2-terminated surface is more active than the other two Fe-terminated surfaces, showing half-metallic properties, similar to bulk Fe3O4. The Fe-tet1-O1-terminated surface, the O-terminated surfaces, and the surfaces with vacancy defects all show metallic properties.