Dynamics of the excitonic coupling in organic crystals

We show that the excitonic coupling in molecular crystals undergoes a very large fluctuation at room temperature as a result of the combined thermal motions of the nuclei. This observation dramatically affects the description of exciton transport in organic crystals and any other phenomenon (like singlet fission or exciton dissociation) that originates from an exciton in a molecular crystal or thin film. This unexpected result is due to the predominance of the short-range excitonic coupling mechanisms (exchange, overlap, and charge-transfer mediated) over the Coulombic excitonic coupling for molecules in van der Waals contact. To quantify this effect we develop a procedure to evaluate accurately the short-range excitonic coupling (via a diabatization scheme) along a molecular dynamics trajectory of the representative molecular crystals of anthracene and tetracene

Charge dynamics in organic photovoltaic materials : interplay between quantum diffusion and quantum relaxation

This paper discusses the mechanism of generation of free charges in organic photovoltaic cells (OPV) from electrostatically bound electron–hole pairs. The efficiency of this process is explained when interfacial charge-transfer (CT) states are generated by direct optical excitation. We used semiclassical quantum dynamics at a short time scale (∼100 fs) and Redfield theory at a relatively long time scale (∼10–100 ps) to cover both the process of dissociation and the relaxation to the lowest energy state. Our calculations suggest that a CT state with an intermediate electron–hole separation can evolve into a charge-separated (CS) state on ultrafast time scales (∼100 fs) as a result of quantum diffusion. On long time scales, however, the CS states ultimately relax to the low-energy CT states due to the interaction with the thermal bath, indicating that the yield of free charge carrier generation is determined by the interplay between ultrafast charge separation, due to quantum diffusion, and the much slower quantum relaxation process

Nonlocal van der Waals Approach Merged with Double-Hybrid Density Functionals: Toward the Accurate Treatment of Noncovalent Interactions

Noncovalent interactions drive the self-assembly of weakly interacting molecular systems to form supramolecular aggregates, which play a major role in nanotechnology and biochemistry. In this work, we present a thorough assessment of the performance of different double-hybrid density functionals (PBE0-DH-NL, revPBE0-DH-NL, B2PLYP-NL, and TPSS0-DH-NL), as well as their parent hybrid and (meta)GGA functionals, in combination with the most modern version of the nonlocal (NL) van der Waals correction. It is shown that this nonlocal correction can be successfully coupled with double-hybrid density functionals thanks to the short-range attenuation parameter b, which has been optimized against reference interaction energies of benchmarking molecular complexes (S22 and S66 databases). Among all the double-hybrid functionals evaluated, revPBE0-DH-NL and B2PLYP-NL behave remarkably accurate with mean unsigned errors (MUE) as small as 0.20 kcal/mol for the training sets and in the 0.25–0.42 kcal/mol range for an independent database (NCCE31). They can be thus seen as appropriate functionals to use in a broad number of applications where noncovalent interactions play an important role. Overall, the nonlocal van der Waals approach combined with last-generation density functionals is confirmed as an accurate and affordable computational tool for the modeling of weakly bonded molecular systems.Financial support by the “Ministerio de Economía y Competitividad” (MINECO) of Spain and the “European Regional Development Fund” through projects CTQ2011-27253, CTQ2012-31914, and Consolider-Ingenio CSD2007-00010 in Molecular Nanoscience is acknowledged. The support of the Generalitat Valenciana (Prometeo/2012/053) is also acknowledged. J.C.S.G. holds a visiting professorship (University of Mons) founded by the Belgian National Fund of Scientific Research (FNRS)

Slow food : restaurante y escuela de cocina en la Albufera de Valencia

[ES] Promocionar los productos naturales de la huerta valenciana y su cocina, luchar contra el abandono de la cultura tradicional y la estandarización de la comida, disfrutar de nuevas experiencias y perspectivas de la restauración desde el cuidado y cultivo de los productos frescos, tratamiento, cocción, presentación y degustación, son algunos de los objetivos que persigue este proyecto. No solo es un restaurante y escuela de cocina sino que también se busca cultivar la relación existente entre turismo y gastronomía, conectando la degustación gastronómica con el paisaje y la cultura.[EN] Promoting the natural products of the Valencian orchard and its cuisine, fighting against the abandonment of the traditional culture and the standarization of food, enjoying new experiences and perspectives of restaurant management from the careness and harvest of fresh products, treatment, cooking, presentation and degustation, are some of the objectives that are pursued in this project. It is not only a restaurant and a cuisine school but it is also the researching at the harvesting of the existent relationship between tourism and gastronomy throughout the necessary connexion of the gastronomy degustation with the landscape and the culture.Aragó Díaz, JA. (2019). Slow food : restaurante y escuela de cocina en la Albufera de Valencia. http://hdl.handle.net/10251/123529TFG

Spatial point process modeling applied to the assessment of risk factors associated to forest wildfires incidence in Castellón, Spain

During the last decades the Mediterranean zone in Europe has experienced an increment in the incidence of forest wildfires. This increase is partly explained by higher mean temperature and lower relative humidity, while socioeconomic change has lead to the abandonment of farms, resulting in an increase in an unusual accumulation of forest fuels, increasing the risk of wildfires. Mapping wildfire risk is highly important because wildfires are known to potentially lead to landscape changes and to modify fire regime by inducing potential changes in vegetation composition. Also, they pose a hazard to human property and life. Maps of wildfire risk based on statistical models provide a measure of uncertainty for the inferences derived from such risk maps, leaving a quantitative error margin for managers and decision takers. Further, some of the model parameters often have a physical or a biological interpretation which can give ecologists and forest engineers answers about scientific questions of interest. In this paper, we analyze the incidence of wildfires in the province of Castellón in Spain in order to identify risk factors associated with wildfire incidences during the years 2001–2006. We used the discrete nature of wildfire events to build such models using point process theory and methods and included information about elevation, slope, aspect, land use and distance to nearest road as covariates in our modeling process. Our results show that wildfire risk in Castellón is associated with all the covariates considered and that three land-use categories have the highest risk of wildfire incidence. Also, wildfire incidences are not independent and some degree of interaction exists, which indicates that the commonly used Poisson point process models are not applicable in this case, but instead area-interaction models should be considered

Integration of Environmental Models in Spatial Data Infrastructures: A Use Case in Wildfire Risk Prediction

Achieving sustainable growth in our society implies monitoring our environment in order to measure human impact and detect relevant changes and detrimental driving factors such as wildfires and desertification. In order for experts to perform environmental modelling they need to be able to access data and models in an efficient and interoperable manner as well as share their findings to assist other professionals in decision making. In the current information society, distributed information systems are essential for sharing digital resources such as data and tools. Advances in Service-Oriented Architectures (SOA) allow for the distribution and accessibility of on-line resources such as data and tools, which served through standards-based services improve the sharing of data, models and models results. This research presents a service-oriented application that addresses the issues of interoperable access to environmental modelling capabilities as well as the mechanisms to share their results an efficiently throughout interoperable components. The aim is twofold, first we present different models for multi-scale forest fire risk prediction based on spatial point processes, and second we provide this functionality as a distributed application, that, based on international standards, such as those offered by the Open Geospatial Consortium (OGC), improves interoperable access to these models as well as the publication of the results to be shared with other interested stakeholders

Excitonic couplings between molecular crystal pairs by a multistate approximation

In this paper, we present a diabatization scheme to compute the excitonic couplings between an arbitrary number of states in molecular pairs. The method is based on an algebraic procedure to find the diabatic states with a desired property as close as possible to that of some reference states. In common with other diabatization schemes, this method captures the physics of the important short-range contributions (exchange, overlap, and charge-transfer mediated terms) but it becomes particularly suitable in presence of more than two states of interest. The method is formulated to be usable with any level of electronic structure calculations and to diabatize different types of states by selecting different molecular properties. These features make the diabatization scheme presented here especially appropriate in the context of organic crystals, where several excitons localized on the same molecular pair may be found close in energy. In this paper, the method is validated on the tetracene crystal dimer, a well characterized case where the charge transfer (CT) states are closer in energy to the Frenkel excitons (FE). The test system was studied as a function of an external electric field (to explore the effect of changing the relative energy of the CT excited state) and as a function of different intermolecular distances (to probe the strength of the coupling between FE and CT states). Additionally, we illustrate how the approximation can be used to include the environment polarization effect

Exciton dynamics in phthalocyanine molecular crystals

The exciton transport properties of an octa(butyl)-substituted metal-free phthalocyanine (H2-OBPc) molecular crystal have been explored by means of a combined computational (molecular dynamics and electronic structure calculations) and theoretical (model Hamiltonian) approximation. The excitonic couplings in phthalocyanines, where multiple quasi-degenerate excited states are present in the isolated chromophore, are computed with a multistate diabatization scheme which is able to capture both short- and long-range excitonic coupling effects. Thermal motions in phthalocyanine molecular crystals at room temperature cause substantial fluctuation of the excitonic couplings between neighboring molecules (dynamic disorder). The average values of the excitonic couplings are found to be not much smaller than the reorganization energy for the excitation energy transfer, and the commonly assumed incoherent regime for this class of materials cannot be invoked. A simple but realistic model Hamiltonian is proposed to study the exciton dynamics in phthalocyanine molecular crystals or aggregates beyond the incoherent regime

Electrical two-qubit gates within a pair of clock-qubit magnetic molecules

Enhanced coherence in HoW10 molecular spin qubits has been demonstrated by use of clock-transitions (CTs). More recently it was shown that, while operating at the CTs, it was possible to use an electrical field to selectively address HoW10 molecules pointing in a given direction, within a crystal that contains two kinds of identical but inversion-related molecules. Herein we theoretically explore the possibility of employing the electric field to effect entangling two-qubit quantum gates within a 2-qubit Hilbert space resulting from dipolar coupling of two CT-protected HoW10 molecules in a diluted crystal. We estimate the thermal evolution of T1, T2, find that CTs are also optimal operating points from the point of view of phonons, and lay out how to combine a sequence of microwave and electric field pulses to achieve coherent control within a switchable two-qubit operating space between symmetric and asymmetric qubit states that are protected both from spin-bath and from phonon-bath decoherence. This two-qubit gate approach presents an elegant correspondence between physical stimuli and logical operations, meanwhile avoiding any spontaneous unitary evolution of the qubit states. Finally, we found a highly protected 1-qubit subspace resulting from the interaction between two clock molecules

Do investors in Spain react to news on sustainability and corporate social responsibility?

We analyse whether sustainability and corporate social responsibility-related news affects returns of stocks traded on the Spanish stock market. We used event methodology and an approach consistent with the active management of investment portfolios. Results show that in the short term, investors do not consider these news items to be relevant, and they therefore have no effect on the price of the stocks analysed. This result holds when the study is conditioned to the type of news (positive or negative) and whether or not the stocks belong to an index formed following socially responsible investment criteri