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Time dependent density functional theory (TD-DFT) calculations have been carried out to study the electronic structure and the optical properties of five coumarin based dyes: C343, NKX-2311, NKX-2586, NKX-2753 and NKX-2593. We have found out that the position and width of the first band in the electronic absorption spectra, the absorption threshold and the LUMO energy with respect to the conduction band edge are key parameters in order to establish some criteria that allow evaluating the efficiency of coumarin derivatives as sensitizers in Dye Sensitized Solar Cells (DSSC). Those criteria predict the efficiency ordering for the coumarin series in good agreement with the experimental evidence. Presumably, they might be used in the design of new efficient organic based DSSC.

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Dissociation mechanisms for methanol and water on stoichiometric and defective TiO2 (110) surfaces have been clarified from periodic density functional calculations. When the molecules are adsorbed on an oxygen vacancy, the most favorable route to dissociation is an indirect mechanism involving, initially, the formation of an intermediate hydroxyl group on in-plane oxygen, followed by the hydrogen transfer to a neighbor bridging oxygen. Since the transient species lifetime is short, they are difficult to be detected. At variance, dissociation on stoichiometric surfaces proceeds readily through a direct hydrogen transfer process from the adsorbate to bridging oxygen. However, the energy barrier for the recombination is low and the species can return to the initial state.

We have carried out first-principles density functional calculations for clusters of the coinage metals containing thirteen atoms (M13, where M=Cu, Ag, or Au). We find that for this geometric “magic number” the low energy isomers are actually disordered, forming almost a continuous distribution as a function of energy.