Partial dissociation of Water on Fe$_3$O$_4$ (001): Adsorbate Induced Charge and Orbital Order

Besides potential applications in spintronics, magnetite plays an important role in many environmental redox reactions. Using density-functional theory together with an on-site Coulomb repulsion term (GGA+$U$), we investigate the interaction of water and its influence on the electronic properties and surface reconstruction of Fe$_3$O$_4$(001). The surface phase diagram, compiled within the framework of {\sl ab initio} atomistic thermodynamics, reveals dissociative adsorption especially at surface defect sites. At higher water vapour pressures a partial dissociation sets in where a chain of hydrogen bonded H$_2$O and OH groups forms. The mixed adsorption mode and a suppression of the $(\sqrt{2}\times \sqrt{2})R45^{\circ}$ reconstruction is confirmed by a quantitative low energy electron diffraction analysis. The defects and adsorbates induce a unique charge and orbital order on the Fe$_3$O$_4$(001) surface[1]. \begin{enumerate} \item N.Mulakaluri {\sl et al.}, Phys. Rev. Lett \textbf{103}, 176102 (2009). \end{enumerate}