The structure and electronic properties of different terminations of the α-Fe(2)O(3)(0001) surface were studied with spin-polarized density functional theory (DFT) and the DFT + U method accounting for the effect of strong on-site Coulomb correlations. The results for lattice relaxation, electronic and magnetic properties are presented and discussed. Though the DFT and DFT + U methods provide qualitatively very similar surface geometries they differ very much in the prediction of the electronic and magnetic properties, and the surface energetics of the clean α-Fe(2)O(3)(0001). The most stable single iron terminated (0001) surface and the oxygen-rich termination were chosen to study Au and Pd atom adsorption. The results show that both Au and Pd bind strongly to hematite surfaces and induce large changes in their geometry. The DFT + U bonding is weaker by 0.3-0.6 eV than DFT on the iron terminated surface and about 2 eV stronger on the oxygen terminated one. The binding is stronger for Pd than Au and for both adsorbates is distinctly stronger at the oxygen than at the iron terminated surface. On the iron terminated surface the adsorption binding energy per adatom increases both with Au and Pd coverage, whereas for the oxygen terminated one the opposite trend is observed.

Density functional theory and a pseudopotential plane wave method are applied to study electronic and structural properties of the defect-free TiO(2)(110) surface. The variations of the surface energy, work function, and atomic displacements are examined for partially and fully relaxed slabs modelling the rutile (110) surface, and consisting of up to 33 atomic layers. Relatively small relaxations of atomic positions in the outermost layers have a strong influence on the calculated surface energies and work functions. The effect of nonequivalence of the odd-even layer terminations is explored. A simple method is proposed which allows one to estimate accurate surface energies for relaxed systems from calculations for partially relaxed slabs.

This is the first of two papers dealing with the adsorption of Au and formation of Aun nanostructures (n = 1-4) on hematite (0001) surface and adsorption of CO thereon. The stoichiometric Fe-terminated (0001) surface of hematite was investigated using density functional theory in the generalized gradient approximation of Perdew-Burke-Ernzerhof (PBE) form with Hubbard correction U, accounting for strong electron correlations (PBE+U). The structural, energetic, and electronic properties of the systems studied were examined for vertical and flattened configurations of Aun nanostructures adsorbed on the hematite surfaces. The flattened ones, which can be viewed as bilayer-like structures, were found energetically more favored than vertical ones. For both classes of structures the adsorption binding energy increases with the number of Au atoms in a structure. The adsorption of Aun induces charge rearrangement at the Aun/oxide contact which is reflected in work function changes. In most considered cases Aun adsorption increases the work function. A detailed analysis of the bonding electron charge is presented and the corresponding electron charge rearrangements at the contacts were quantified by a Bader charge analyses. The interaction of a CO molecule with the Aun nanostructures supported on α-Fe2O3 (0001) and the oxide support was studied. It is found that the CO adsorption binding to the hematite supported Aun structures is more than twice as strong as to the bare hematite surface. Analysis of the Bader charges on the atoms showed that in each case CO binds to the most positively charged (cationic) atom of the Aun structure. Changes in the electronic structure of the Aun species and of the oxide support, and their consequences for the interactions with CO, are discussed.

The spin-density functional theory (DFT) and DFT+U with Hubbard U term accounting for onsite Coulomb interactions were applied to investigate structure, stability, and electronic properties of different terminations of the Fe3O4(111) surface. All terminations of the ferrimagnetic Fe3O4(111) surface exhibit very large (up to 90%) relaxations of the first four interlayer distances, decreasing with the oxide layer depth. Our calculations predict the iron terminated surface to be most stable in a wide range of the accessible values of the oxygen chemical potential. The adsorption of Au and Pd on two stable Fe-and O-terminated surfaces is studied. Our results show that Pd binds stronger than Au both to the Fe-and O-terminated surface. DFT+U gives stronger bonding than DFT. The bonding of both adsorbates to the O-terminated magnetite surface is by 1.5-2.5 eV stronger than to the Fe-terminated surface.

Polar ionic surfaces with bulk termination are inherently unstable because of their diverging electrostatic surface energy. Nevertheless, they are frequently observed in nature, mainly because of charge neutralization by adsorbates, but occur also under atomically clean conditions. Several mechanisms have been invoked to explain the stability of atomically clean polar surfaces, but the frequently observed periodic nanoscale pattern formation has not yet been explained. Here we propose that long-range interactions between alternating electropositive and electronegative regions of different surface terminations minimize the electrostatic energy of the surface and thus stabilize the nanoscale pattern. This is illustrated using the example of polar Fe oxide surfaces by combining scanning tunneling microscopy and spectroscopy results with results from density functional theory-based calculations and dipole–dipole interaction models