The ab initio full-potential linearized-augmented-plane-wave method for a free-slab geometry was used to calculate the electronic structure and geometry of a clean Ti02 (110) rutile surface. Surface induced states were found in the density of states, such as an s-like surface state at -15 eV. Band bending states of width 0.5 eV appear just below the Fermi energy, in agreement with photoemission experiments. The positions of the atoms in the surface and subsurface layers and the corresponding change of Ti-0 bond lengths were derived by total-energy minimization. In general, downward relaxations were obtained for which the Svefold-coordinated Ti experienced the largest relaxation of -0.180 A, whereas 0 the second most important relaxation efFect, -0.156 A, occurred for the surface O. The calculated Ti-0 bond lengths are in very good agreement with experimental data for the Ti02 (100) surface. The calculated work function 6.79 eV compares favorably with the experimental result of 6.83 eV. Based on an extension of density-functional theory to excited states the valenceand conduction-band gap was calculated to be 1.99 eV, which is in reasonable agreement with the experimental gap of 2.6 eV when compared to the one-particle band gap of 0.65 eV.
We present a model combining ab initio concepts and molecular dynamics simulations for a more realistic treatment of complex adsorption processes. The energy, distance, and orientation of water molecules adsorbed on stoichiometric and reduced rutile TiO(2)(110) surfaces at 140 K are studied via constant temperature molecular dynamics simulations. From ab initio calculations relaxed atomic geometries for the surface and the most probable adsorption sites were derived. The study comprises (i) large two-dimensional surface supercells, providing a realistically low concentration of surface oxygen defects, and (ii) a water coverage sufficiently large to model the onset of the growth of a bulk phase of water on the surface. By our combined approach the influence of both, the metal oxide surface, below, and the bulk water phase, above, on the water molecules forming the interface between the TiO(2) surface and the water bulk layer is taken into account. The good agreement of calculated adsorption energies with experimental temperature programmed desorption spectra demonstrates the validity of our model.
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