Jahn-Teller stabilization of a "polar" metal oxide surface: Fe3O4(001)
  Using ab initio thermodynamics we compile a phase diagram for the surface of Fe3O4(001) as a function of temperature and oxygen pressures. A hitherto ignored polar termination with octahedral iron and oxygen forming a wave-like structure along the [110]-direction is identified as the lowest energy configuration over a broad range of oxygen gas-phase conditions. This novel geometry is confirmed in a x-ray diffraction analysis. The stabilization of the Fe3O4(001)-surface goes together with dramatic changes in the electronic and magnetic properties, e.g., a halfmetal-to-metal transition. 
R. Pentcheva, F. Wendler, H.L. Meyerheim, W. Moritz, N. Jedrecy, and   M. Scheffler