Long-range parameter optimization for a better description of potential energy surfaces using Density Functional Theory.

The advance of computing and the development of modern quantum chemistry models such as Density Functional Theory (DFT) have allowed scientists to perform fast in silico studies with accurate results. It also allowed for the achievement of empirically unattainable quantities such as Potential Energy Surfaces (PES), a fundamental construct in various applications, such as the study of weakly bound systems. One of DFT's current weaknesses is a reliable description of PESs, due to a lack of suitable exchange-correlation functionals. In general, other post-Hartree-Fock methods are employed, such as n th-order Møller-Plesset's Perturbation Theory (MPn) or Coupled Cluster Theory (CCSD(T)) with large basis sets. Despite producing good results, these methods demand much computational power when applied to large systems. This work presents a novel approach of PES description of the H2O2-Kr system using DFT by optimizing a long-range parameter present in some DFT functionals, obtaining results similar to those of the MPn methods with somewhat less computational time necessary. Graphical Abstract By optimizing the omega value of certain functionals, DFT can describe PESs with accuracy comparable to MP4 methods.

Interfacial versus Bulk Properties of Hole-Transporting Materials for Perovskite Solar Cells: Isomeric Triphenylamine-Based Enamines versus Spiro-OMeTAD.

Here, we report on three new triphenylamine-based enamines synthesized by condensation of an appropriate primary amine with 2,2-diphenylacetaldehyde and characterized by experimental techniques and density functional theory (DFT) computations. Experimental results allow highlighting attractive properties including solid-state ionization potential in the range of 5.33-5.69 eV in solid-state and hole mobilities exceeding 10-3 cm2/V·s, which are higher than those in spiro-OMeTAD at the same electric fields. DFT-based analysis points to the presence of several conformers close in energy at room temperature. The newly synthesized hole-transporting materials (HTMs) were used in perovskite solar cells and exhibited performances comparable to that of spiro-OMeTAD. The device containing one newly synthesized hole-transporting enamine was characterized by a power conversion efficiency of 18.4%. Our analysis indicates that the perovskite-HTM interface dominates the properties of perovskite solar cells. PL measurements indicate smaller efficiency for perovskite-to-new HTM hole transfer as compared to spiro-OMeTAD. Nevertheless, the comparable power conversion efficiencies and simple synthesis of the new compounds make them attractive candidates for utilization in perovskite solar cells.

Kinetic Monte Carlo model for the COVID-19 epidemic: Impact of mobility restriction on a COVID-19 outbreak.

As the coronavirus disease 2019 (COVID-19) spreads worldwide, epidemiological models have been employed to evaluate possible scenarios and gauge the efficacy of proposed interventions. Considering the complexity of disease transmission dynamics in cities, stochastic epidemic models include uncertainty in their treatment of the problem, allowing the estimation of the probability of an outbreak, the distribution of epidemic magnitudes, and their expected duration. In this sense, we propose a kinetic Monte Carlo epidemic model that focuses on demography and on age-structured mobility data to simulate the evolution of the COVID-19 outbreak in the capital of Brazil, Brasilia, under several scenarios of mobility restriction. We show that the distribution of epidemic outcomes can be divided into short-lived mild outbreaks and longer severe ones. We demonstrate that quarantines have the effect of reducing the probability of a severe outbreak taking place but are unable to mitigate the magnitude of these outbreaks once they happen. Finally, we present the probability of a particular trajectory in the epidemic progression resulting in a massive outbreak as a function of the cumulative number of cases at the end of each quarantine period, allowing for the estimation of the risk associated with relaxing mobility restrictions at a given time.

Efficient Exciton Diffusion and Resonance-Energy Transfer in Multilayered Organic Epitaxial Nanofibers.

Multilayered epitaxial nanofibers are exemplary model systems for the study of exciton dynamics and lasing in organic materials because of their well-defined morphology, high luminescence efficiencies, and color tunability. We use temperature-dependent continuous wave and picosecond photoluminescence (PL) spectroscopy to quantify exciton diffusion and resonance-energy transfer (RET) processes in multilayered nanofibers consisting of alternating layers of para-hexaphenyl (p6P) and α-sexithiophene (6T) serving as exciton donor and acceptor material, respectively. The high probability for RET processes is confirmed by quantum chemical calculations. The activation energy for exciton diffusion in p6P is determined to be as low as 19 meV, proving p6P epitaxial layers also as a very suitable donor material system. The small activation energy for exciton diffusion of the p6P donor material, the inferred high p6P-to-6T resonance-energy-transfer efficiency, and the observed weak PL temperature dependence of the 6T acceptor material together result in an exceptionally high optical emission performance of this all-organic material system, thus making it well suited, for example, for organic light-emitting devices.