In this work, we present binding energies of acetic acid on the (110), (100), and (011) surfaces of rutile TiO 2 calculated with the two density functional theory (DFT) exchange-correlation functionals PBE and PBEsol. It is shown that the binding energies can be influenced, in this case slightly reduced for all three surfaces, via preadsorption of hydrogen. Additionally, we tested the performance of the densityfunctional based tight-binding (DFTB) method applied to these adsorbate systems. Analysis of the electronic density of states shows that DFTB provides qualitatively comparable results to DFT calculations as long as the Fermi energy level remains within the band gap.

Oxygen-deficient TiO2 in the rutile structure as well as the Ti3O5 Magnéli phase is investigated within the charge self-consistent combination of density functional theory (DFT) with dynamical mean-field theory (DMFT). It is shown that an isolated oxygen vacancy (VO) in titanium dioxide is not sufficient to metallize the system at low temperatures. In a semiconducting phase, an ingap state is identified at ε IG ∼ −0.75 eV in excellent agreement with experimental data. Bandlike impurity levels, resulting from a threefold VO-Ti coordination as well as entangled (t2g, eg) states, become localized due to site-dependent electronic correlations. Charge localization and strong orbital polarization occur in the VO-near Ti ions, which details can be modified by a variation of the correlated subspace. At higher oxygen vacancy concentration, a correlated metal is stabilized in the Magnéli phase. A VO-defect rutile structure of identical stoichiometry shows key differences in the orbital-resolved character and the spectral properties. Charge disproportionation is vital in the oxygen-deficient compounds, but obvious metal-insulator transitions driven or sustained by charge order are not identified. arXiv:1703.05543v2 [cond-mat.mtrl-sci]

Acetone adsorbed on rutile TiO 2 nanoparticles was investigated with respect to its energetic, vibrational, and chemical properties. Temperature-dependent ultrahigh-vacuum Fourier transform infrared spectroscopy measurements for different acetone dosages (4.5− 900 L) give insights into the acetone adsorption behavior. Those experiments indicate thermal-induced reactions of acetone on rutile TiO 2 surfaces yielding new species. Density functional theory calculations were performed to investigate acetone adsorption on rutile TiO 2 (110). Particularly, the importance of sampling the adsorption configuration space is shown. Adsorption geometries that are energetically significantly more favorable than the commonly used high-symmetry configurations are presented. To facilitate the comparability to the experiment, theoretical infrared spectra were computed using density functional perturbation theory for various acetone adsorption geometries using different exchangecorrelation functionals. Additionally, computational spectra were obtained for several species which are potential products from reactions of acetone on TiO 2 surfaces. The investigated species are η 2 -acetate, η 2 -diolate, η 1 -enolate, and mesityl oxide. For η 1acetone, experimental and calculated spectra fit well for low temperatures, whereas for elevated temperatures, emerging bands indicate the formation of diolate.

Density functional theory (DFT) has been applied to elucidate the adsorption structures and energetics of benzoic acid on TiO 2 (110), (100), and (011) rutile surfaces. We demonstrate that ab initio calculations of interacting carboxylic acids require an exchangecorrelation functional with van der Waals (vdW) correction to yield reliable results, even for very small aliphatic species like acetic acid. On the (110) surface, benzoates dimerize due to intermolecular vdW interaction and form a 2 × 2 superstructure, which explains experimental findings already reported in the literature. The lateral vdW attraction between benzoates is even enhanced on ( 100) and ( 011) surfaces because of advantageous substrate periodicities, resulting essentially in only one geometrical adsorbate species.

The results of a comprehensive and systematic ab-initio based ground-state search for the structural arrangement of oxygen vacancies in rutile phase TiO 2 provide new insights into their memristive properties. We find that O vacancies tend to form planar arrangements which relax into structures exhibiting metallic behavior. These meta-stable arrangements are structurally akin to, yet distinguishable from the Magnéli phase. They exhibit a more pronounced metallic nature, but are energetically less favorable. Our results confirm a clear structure-property relationship between segregated oxygen vacancy arrangement and metallic behavior in reduced oxides. 1 arXiv:1509.08412v2 [cond-mat.mtrl-sci]