The adsorption of two different organic molecules cyanidin glucoside (C21O11H20) and TA-St-CA on anatase (101) and (001) nanowires has been investigated using the standard and the range separated hybrid density functional theory calculations. The electronic structures and optical spectra of resulting dye–nanowire combined systems show distinct features for these types of photochromophores. The lowest unoccupied molecular orbital of the natural dye cyanidin glucoside is located below the conduction band of the semiconductor while, in the case of TA-St-CA, it resonates with the states inside the conduction band. The wide-bandgap anatase nanowires can be functionalized for solar cells through electron-hole generation and subsequent charge injection by these dye sensitizers. The intermolecular charge transfer character of Donor-π-Acceptor type dye TA-St-CA is substantially modified by its adsorption on TiO2 surfaces. Cyanidin glucoside exhibits relatively stronger anchoring on the nanowires through its hydroxyl groups. The atomic structures of dye–nanowire systems re-optimized with the inclusion of nonlinear solvation effects showed that the binding strengths of both dyes remain moderate even in ionic solutions.

The electronic and optical properties of thin anatase TiO2 (1 0 1) and (0 0 1) nanowires have been investigated using the screened Coulomb hybrid density functional calculations. For the bare nanowires with sub-nanometer diameters, the calculated band gaps are larger relative to the bulk values due to size effects. The role of organic light harvesting sensitizers on the absorption characteristics of the anatase nanowires has been examined using the hybrid density functional method incorporating partial exact exchange with range separation. For the lowest lying excitations, directional charge redistribution of tetrahydroquinoline (C2-1) dye shows a remarkably different profile in comparison to a simple molecule which is chosen as the coumarin skeleton. The binding modes and the adsorption energies of C2-1 dye and coumarin core on the anatase nanowires have been studied including non-linear solvation effetcs. The calculated optical and electronic properties of the nanowires with these two different types of sensitizers have been interpreted in terms of their electron-hole generation, charge carrier injection and recombination characteristics. (C) 2015 Elsevier B.V. All rights reserved.

The adsorption of organic molecules coumarin and the donor-p-acceptor type tetrahydroquinoline (C2-1) on anatase (101) and (001) nanowires has been investigated using screened Coulomb hybrid density functional theory calculations. Simple coumarin core forms a single bond with the TiO2. C2-1 exhibits a bidentate mode giving rise to much stronger adsorption energies on the nanowire surface. Nonlinear solvation effects on the binding characteristics of the dye chromophores on the nanowire facets have also been examined. These two dye sensitizers show different electronic charge distributions for the highest occupied and the lowest unoccupied molecular states. We studied the electronic structures in terms of the positions of the band edges and adsorbate-related gap states and their effect on the absorption spectra of the dyenanowire combined systems. These findings were interpreted and discussed from the viewpoint of better light harvesting and charge separation as well as in relation to more efficient charge carrier injection into the semiconductor nanowire

Tunability of the photoabsorption and directional charge injection characteristics of Bodipy-based dye molecules with different carbonyl groups make them promising candidates for photovoltaic applications. In order to study the effect of screening in the Coulomb interaction on the electronic and optical properties of two Bodipy derivatives, we have used linear response time-dependent and exact exchange hybrid density functional approaches. The effect of linear and non-linear solvation models on the electrochemical properties of the dyes has also been discussed.

The electronic properties of quasi-one-dimensional anatase TiO2 nanostructures, in the form of thin nanowires having (101) and (001) facets, have been systematically investigated using the standard, hybrid density functional and quasiparticle calculations. Their visible photoabsorption characteristics have also been studied at these levels of theories. The thin stoichiometric nanowire models are predicted to have larger band gaps relative to their bulk values. The band-gap-related features appear to be better described with the screened Coulomb hybrid density functional method compared to the standard exchange-correlation schemes. Depending on the self-consistency in the perturbative GW methods, even larger energy corrections have been obtained for the band gaps of both (101) and (001) titanium dioxide nanowires.

Physically reasonable electronic structures of reconstructed rutile TiO_2(110)-(1x2) surfaces were studied using density functional theory (DFT) supplemented with Hubbard U on-site Coulomb repulsion acting on the d electrons, so called as the DFT+U approach. Two leading reconstruction models proposed by Onishi--Iwasawa and Park et al. were compared in terms of their thermodynamic stabilities.

The adsorption profiles and electronic structures of Pt-n(n = 1-4) clusters on stoichiometric, reduced and reconstructed rutile TiO2(110) surfaces were systematically studied using on site d-d Coulomb interaction corrected hybrid density-functional-theory (DFT) calculations. The atomic structure of small Pt cluster adsorbates mainly depends on the stoichiometry of the corresponding titania support. The cluster shapes on the bulk terminated ideal surface look like their gas phase low-energy structures. However, for instance, they get significantly distorted on the reduced surfaces with increasing oxygen vacancies. On nonstoichiometric surfaces, Pt-Ti coordination becomes dominant in the determination of the adsorption geometries. The electronic structure of Pt-n/TiO2(110) systems cannot be correctly described by pure DFT methods, particularly for nonstoichiometric cases due to the inappropriate treatment of the correlation for d electrons. We performed DFT + U calculations to give a reasonable description of the reconstructed rutile (110) surface. Pt clusters induce local surface relaxations that influence band edges of titania support and bring a number of band-gap states depending on the cluster size. Significant band gap narrowing occurs upon Pt-n-surface interaction due to adsorbate driven states on the bulk terminated and reduced surfaces. On the other hand, they give rise to a band-gap widening associated to partial reoxidation of the reconstructed surface. No metallization arises even for Pt-4 on rutile.