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A theoretical study was carried out for the first time in a series of two nanocomposite semiconducting systems (PbS) 4 @(TiO 2 ) 38 . We stabilized two structures of TiO 2 using a simulated annealing procedure with Molecular Dynamics as a first approach and the second model was optimized at the PBE level of theory, as benchmarking. An amorphous and anatase structures were found for both methodologies, respectively. We adopted the cubic structure of the (PbS) 4 quantum dot as suggested by experimental data. The DOS of the isolated systems were assessed and also those of the composites (PbS) 4 @(TiO 2 ) 38 . Adsorption energies on both systems were estimated and an attraction with a certain degree of covalency was found for the (PbS) 4 at the TiO 2 anatase model system. A weaker interaction of the electrostatic-type was found with the TiO 2 amorphous configuration. In both systems, the attraction is favored in S Ti bond pairs. The DOS for the composite systems presents a different nature for the amorphous and anatase cases that is evidenced in the size of the band gaps. The (PbS) 4 @(TiO 2 ) 38 anatase composite systems results in a more favorable electronic structure that may readily provide fundamental data to develop and design photocatalytic devices for hydrogen production, energy storage and photovoltaic applications. [ABSTRACT FROM AUTHOR]

This work gives new evidence on the structural properties of tetragonal hybrid perovskites obtained from different experimental routes of synthesis, and the theoretical elucidation of their electronic structure properties in accordance to the formation of the energy band gaps. Two different synthesis routes to prepare hybrid perovskites of the form (CH 3 NH 3 PbI 3) have been performed. The final crystal structure depends on the conditions of the preparation method that give the perovskite a twisted or regular molecular structure. This was certified by the structural analysis, normal modes of vibration, and opto-electronic properties. Moreover, the elucidation of electronic structure properties were also analyzed by a first principles study. That is, density functional theory (DFT) calculations revealed the structure configuration of twisted hybrid perovskites CH 3 NH 3 PbI 3 , in combination with XRD evidence. The electronic structure properties of the systems under study are mainly ruled by the geometrical disposition of the organic cation, whose different degrees of freedom are intimately related to the size of the energy band gap, and also to the magnitude of the work function. The DFT analysis with the experimental characterization of these hybrid perovskite systems could aid to tailor novel materials intended to be applied in the new generation of solar cell devices. That is, our combined methodology could contribute to modify the structure of perovskites with improved electronic properties for solar energy applications. [Display omitted] • The slow solvent evaporation process showed an iodine atom deviation. • CH 3 NH 3 PbI 3 optoelectronic properties were impacted by two synthesis methods. • DFT calculations revealed that the organic cation plays a role on gap formation. • Theoretical work functions are sensitive to the atomic interactions with the substrate. • Absorption spectra showed that twisted perovskites could act as an absorber material. [ABSTRACT FROM AUTHOR]

A Density Functional study predicting a heterogeneous-catalyzed reaction to obtain biodiesel was performed. Triacetin simulated triglycerides in the presence of an Au(1 1 1) surface as the heterogeneous catalyst. Methoxy was implemented as alcohol solvent to understand the reaction trajectory along a three-step transesterification process. Reactants and products in the three-step process are adsorbed on the Au substrate through non-covalent interactions of the electrostatic-type, which are also mediated by a van der Waals attraction. Density of states indicated that the electronic structure nature of Au is preserved after the interaction with the organic moieties. This may be addressed to an enhanced stability of the Au(1 1 1) catalyst through the overall reaction. Charge transfer analysis revealed that the Au surface oxidation aids in the transesterification of triacetin and evidences that gold plays an important role in this catalytic process. Such results may provide fundamental insights into the design of heterogeneous catalysts for biodiesel production. [ABSTRACT FROM AUTHOR]

Organic solar cell nanomaterials are molecular systems that have been recently incorporated in devices with remarkable properties and high efficiencies. A systematic theoretical study based on density functional theory and non-equilibrium Green's functions was performed to elucidate the electron transport behavior on solar cell materials. The I − V profiles based on the transmission obtained from the electronic density revealed an appropriate performance in simulated conditions of sunlight irradiation, while in dark conditions such systems may behave as a diode. The current methodology may represent a tool to select and design high performance materials for the new generation of solar cell devices. [Display omitted] • Organic photovoltaic molecules were screened by their photoisomerization properties. • DFT revealed the transmission behavior at ground/excited states in screened systems. • Ground and excited states may represent dark/illumination conditions, respectively. • Electron transport in OPV systems could be finely simulated with a ballistic model. • The theoretical model may aid to identify OPV systems with improved performance. [ABSTRACT FROM AUTHOR]

[Display omitted] • Photocatalytic potential of the Cu 2 O for (1 0 0), (1 1 0) and (1 1 1) facets is explored. • Cu 2 O(1 0 0) facet shows a high photocatalytic potential in the conversion of CO 2. • The reaction mechanism of the CO 2 towards methanol and methane is evaluated. • Simulations aids to understand the efficient conversion of CO 2 on the Cu 2 O(1 0 0) facet. In this work, Density Functional Theory (DFT) calculations were performed to elucidate the photocatalytic potential of Cu 2 O surfaces. Three slab models of the (1 0 0), (1 1 0) and (1 1 1) facets were studied by considering their optical and electronic structure properties, and photocatalytic potential. The results showed that Cu 2 O (1 0 0) and (1 1 1) surfaces e excellent candidates to be used in a photocatalytic processes to reduce CO 2 to form some hydrocarbon derivatives. Based on the photocatalytic potential analysis, the Cu 2 O(1 0 0) slab model was implemented to simulate the CO 2 reduction reaction evolution into methanol and methane with the String methodology. The results showed that such Cu 2 O facet could be efficiently implemented to improve the CO 2 photoreduction process. Additionally, this theoretical model could also be implemented to tailor novel photocatalytic materials to produce sustainable solar fuels. [ABSTRACT FROM AUTHOR]

A systematic theoretical study on graphene oxide model systems was performed with Density Functional Theory (DFT), and supported by experimental evidence. The results revealed that graphene is highly susceptible to be decorated with organic functional groups, which induced the formation of a band gap, and the rising of a novel semiconducting character. This novel property was used to explore the possible photocatalytic potential in the model systems under study. That is, we evaluated work functions to theoretically obtain the energies of the valence band maximum and the conduction band minimum with respect to the normal hydrogen electrode potential. The assessment of UV-vis profile via Time-dependent DFT also showed the potential of the model systems to efficiently absorb sun light irradiation under photocatalytic conditions. Moreover, the results showed that it is possible to tune the photocatalytic potential of the graphene oxide models under study by interchanging the functional groups anchored on the graphene surface, and their corresponding contents ratio. Experimental evidence obtained via the measurement of optoelectronic properties, revealed that it is possible to classify a graphene oxide powder into one of the model systems under study, while a photocatalytic procedure performed in our laboratory, showed the facile photoreduction of formic acid into methanol with such a graphene oxide. Consequently, the prediction of the electronic structure properties is expected. This may represent a tool to design materials based on graphene oxide to be implemented in reactors for photocatalytic applications. [ABSTRACT FROM AUTHOR]