The impact of face-mask mandates on all-cause mortality in Switzerland: a quasi-experimental study.

BACKGROUND: Whereas there is strong evidence that wearing a face mask is effective in reducing the spread of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), evidence on the impact of mandating the wearing of face masks on deaths from coronavirus disease 2019 (COVID-19) and all-cause mortality is more sparse and likely to vary by context. Focusing on a quasi-experimental setting in Switzerland, we aimed to determine (i) the effect of face-mask mandates for indoor public spaces on all-cause mortality; and (ii) how the effect has varied over time, and by age and sex. METHODS: Our analysis exploited the fact that between July and October 2020, nine cantons in Switzerland extended a face-mask mandate at different time points from being restricted to public transportation only to applying to all public indoor places. We used both a Difference-in-Differences approach with fixed-effects for canton and week and an event-study approach. RESULTS: In our main Difference-in-Differences model, the face-mask mandate was associated with a 0.3% reduction in all-cause mortality [95% confidence interval (CI): -3.4% to 2.7%; P = 0.818]. This null effect was confirmed in the event-study approach and a variety of robustness checks. Combining the face-mask mandate with social distancing rules led to an estimated 5.1% (95% CI: -7.9% to -2.4%; P = 0.001) reduction in all-cause mortality. CONCLUSIONS: Mandating face-mask use in public indoor spaces in Switzerland in mid-to-late 2020 does not appear to have resulted in large reductions in all-cause mortality in the short term. There is some suggestion that combining face-mask mandates with social distancing rules reduced all-cause mortality.

Effect of organic cation states on electronic properties of mixed organic-inorganic halide perovskite clusters.

We study the effect of organic cation-centered states in mixed organic-inorganic halide perovskites on the bandstructure and optical properties. Clusters of methylammonium lead iodide (MAPbI3) and bromide (MAPbBr3) and of MAPbI3 (MAPbBr3) in which an organic cation was substituted with formamidinium (FA) and guanidinium (GA) are studied with density functional theory and time-dependent density functional theory. This model permitted comparing bandstructure and optical properties with different organic cations computed with GGA and hybrid functionals. We find that while with MA and GA, cation-centered states are deep in the conduction band, with FA, organic cation-centered states are introduced within as little as 0.5 eV of the conduction band maximum, which are expected to influence electronic and optical properties of perovskites in solar cells and other optoelectronic devices. There is qualitative agreement between a GGA and a hybrid functional; however, the use of a hybrid functional leads to a slightly higher offset of the cation-centered states from the conduction band edge, a different order of electronic states, and much better localization of cation-centered states. Analysis of optical absorption spectra suggests that occupation by photoexcitation of FA-centered states and formation of transient formamidinium species is possible in both I and Br-based perovskites.

First-principles investigation of the Lewis acid-base adduct formation at the methylammonium lead iodide surface.

We have here performed a campaign of ab initio calculations focusing on the anchoring mechanism and adduct formation of some Lewis bases, both aliphatic and aromatic, on a PbI2-rich flat (001) methylammonium lead iodide (MAPI) surface. Our goal is to provide theoretical support to the recently reported experimental techniques of MAPI surface passivation via Lewis acid-base neutralization and similarly of MAI·PbI2·(Lewis base) adduct formation. We tested several X-donor bases (X = :N, :O, :S), paying attention to the thermodynamic stability of the final MAPI·base adducts and to their electronic properties. Factors that impact on the passivation mechanism are the directionality of the Lewis base lone pair and its enhanced/reduced overlap with MAPI Pb p orbitals, the dipole moment of the base and, similarly, the electronegativity of the X donor atom. Also non-covalent interactions, both at the surface side (intra, MAPI) and at the very interface (inter, MAPI·Lewis base), seem to contribute to the stability of the final adducts. Here we show that the thermodynamic stability does not necessarily correspond to the most effective base → acid dative bond formation. Starting from a low coverage (12.5% of the undercoordinated Pb atoms available at the surface are passivated) this paper paves the way towards the study of cooperative and steric effects among Lewis bases at higher coverages representing, to the best of our knowledge, one of the very first studies focusing on the molecular anchoring on the surfaces of this very important class of materials.

The Effects of the Organic-Inorganic Interactions on the Thermal Transport Properties of CH3NH3PbI3.

Methylammonium lead iodide perovskite (CH3NH3PbI3), the most investigated hybrid organic-inorganic halide perovskite, is characterized by a quite low thermal conductivity. The rotational motion of methylammonium cations is considered responsible for phonon transport suppression; however, to date, the specific mechanism of the process has not been clarified. In this study, we elucidate the role of rotations in thermal properties based on molecular dynamics simulations. To do it, we developed an empirical potential for CH3NH3PbI3 by fitting to ab initio calculations and evaluated its thermal conductivity by means of nonequilibrium molecular dynamics. Results are compared with model systems that include different embedded cations, and this comparison shows a dominant suppression effect provided by rotational motions. We also checked the temperature dependence of the vibrational density of states and specified the energy range in which anharmonic couplings occur. By means of phonon dispersion analysis, we were able to fully elucidate the suppression mechanism: the rotations are coupled with translational motions of cations, via which inorganic lattice vibrations are coupled and scatter each other.

Structural and electronic features of small hybrid organic-inorganic halide perovskite clusters: a theoretical analysis.

We herein present the results of a series of calculations performed on some representative cluster models of hybrid organic-inorganic halide perovskites, (MA)jPbkXl (l = 2j + k; MA = methylammonium, +CH3NH3; X = halide). In particular, aimed at finding possible analogies with the bulk, we focused our initial attention on neutral clusters of iodides (X = I) constituted by an increasing number of Pb atoms (k = 1, 2, 8, 12). For the single octahedron (k = 1), we similarly extended our calculations to mixed Br-/I-terminated and fully Br-terminated octahedra, finding similar miscibilities for the two dimensionally different systems (i.e., the cluster and bulk). When increasing the size of the models, we found an unequivocally evident relationship between the total dielectric dipole moment of the investigated cluster and the wavefunction spatial distribution of the frontier molecular orbitals. This result rationalizes the structural and electronic properties of such zero-dimensional systems and supports the results previously obtained via linear scaling ab initio methods for very large supercells, i.e., the localization at the nanoscale of the wavefunction of the frontier orbitals as a function of the local fluctuations of the potential, which are mainly associated with the organic cation orientation.

The mechanism of slow hot-hole cooling in lead-iodide perovskite: first-principles calculation on carrier lifetime from electron-phonon interaction.

We report on an analysis of hot-carrier lifetimes from electron-phonon interaction in lead iodide perovskites using first-principles calculations. Our calculations show that the holes in CsPbI3 have very long lifetimes in the valence band region situated 0.6 eV below the top of the valence band. On the other hand, no long lifetime is predicted in PbI3(-). These different results reflect the different electronic density of states (DOSs) in the valence bands, that is, a small DOS for the former structure while a sharp DOS peak for the latter structure. We propose a reduction of the relaxation paths in the small valence DOS as being the origin of the slow hot-hole cooling. Analyzing the generalized Eliashberg functions, we predict that different perovskite A-site cations do not have an impact on the carrier decay mechanism. The similarity between the DOS structures of CsPbI3 and CH3NH3PbI3 enables us to extend the description of the decay mechanism of fully inorganic CsPbI3 to its organic-inorganic counterpart, CH3NH3PbI3.

Zero-dipole molecular organic cations in mixed organic-inorganic halide perovskites: possible chemical solution for the reported anomalous hysteresis in the current-voltage curve measurements.

Starting from a brief description of the main architectures characterizing the novel solar technology of perovskite-based solar cells, we focus our attention on the anomalous hysteresis experimentally found to affect the measurement of the current-voltage curve of such devices. This detrimental effect, associated with slow dynamic reorganization processes, depends on several parameters; among them, the scan rate of the measurements, the architecture of the cell, and the perovskite deposition rate are crucial. Even if a conclusive explanation of the origin of the hysteresis has not been provided so far, several experimental findings ascribe its origin to ionic migration at an applied bias and dielectric polarization that occurs in the perovskite layer. Consistently, a dipole-moment-reduced cation such as formamidinium ion is experimentally reported to quantitatively reduce the hysteresis from perovskite-based devices. By means of a density-functional theory-based set of calculations, we have predicted and characterized guanidinium ion (GA = (+)[C(NH2)3], a zero-dipole moment cation by symmetry)-based organic-inorganic halide perovskite's structural and electronic properties, speculating that such a cation and the alloys it may form with other organic cations can represent a possible chemical solution for the puzzling issue of the hysteresis.

A density functional tight binding study of acetic acid adsorption on crystalline and amorphous surfaces of titania.

We present a comparative density functional tight binding study of an organic molecule attachment to TiO2 via a carboxylic group, with the example of acetic acid. For the first time, binding to low-energy surfaces of crystalline anatase (101), rutile (110) and (B)-TiO2 (001), as well as to the surface of amorphous (a-) TiO2 is compared with the same computational setup. On all surfaces, bidentate configurations are identified as providing the strongest adsorption energy, Eads = -1.93, -2.49 and -1.09 eV for anatase, rutile and (B)-TiO2, respectively. For monodentate configurations, the strongest Eads = -1.06, -1.11 and -0.86 eV for anatase, rutile and (B)-TiO2, respectively. Multiple monodentate and bidentate configurations are identified on a-TiO2 with a distribution of adsorption energies and with the lowest energy configuration having stronger bonding than that of the crystalline counterparts, with Eads up to -4.92 eV for bidentate and -1.83 eV for monodentate adsorption. Amorphous TiO2 can therefore be used to achieve strong anchoring of organic molecules, such as dyes, that bind via a -COOH group. While the presence of the surface leads to a contraction of the band gap vs. the bulk, molecular adsorption caused no appreciable effect on the band structure around the gap in any of the systems.

Lead-iodide nanowire perovskite with methylviologen showing interfacial charge-transfer absorption: a DFT analysis.

Methylviologen lead-iodide perovskite (MVPb2I6) is a self-assembled one-dimensional (1-D) material consisting of lead-iodide nanowires and intervening organic electron-accepting molecules, methylviologen (MV(2+)). MVPb2I6 characteristically shows optical interfacial charge-transfer (ICT) transitions from the lead-iodide nanowire to MV(2+) in the visible region and unique ambipolar photoconductivity, in which electrons are transported through the three-dimensional (3-D) organic network and holes along the 1-D lead-iodide nanowire. In this work, we theoretically study the electronic band-structure and photocarrier properties of MVPb2I6 by density functional theory (DFT) calculations. Our results clearly confirm the experimentally reported type-II band alignment, whose valence band mainly consists of 5p (I) orbitals of the lead-iodide nanowires and the conduction band of the lowest unoccupied molecular orbital of MV(2+). The DFT calculation also reveals weak charge-transfer interactions between the lead-iodide nanowires and MV(2+). In addition, the electronic distributions of the valence and conduction bands indicate the 3-D transport of electrons and 1-D transport of holes, supporting the reported experimental result.

Unraveling the adsorption mechanism of aromatic and aliphatic diols on the TiO2 surface: a density functional theory analysis.

Understanding the adsorption mechanism of organic molecules on inorganic semiconductors is of great importance for generating and control functions in organic-inorganic materials. Here we have comprehensively investigated, by means of the density functional theory, the adsorption structure and energetic stability of aliphatic and aromatic diols on TiO2 using ethylene glycol, 1,2-n-decanediol, and catechol. Our calculations clearly show that the non-dissociative bidentate adsorption is more stable than the dissociative one for the aliphatic diol, both at low and high coverage conditions, result far differently from many other chemical anchor cases for which the dissociative mechanism usually prevails. On the other hand, for catechol the dissociative bidentate is the most stable at low coverage conditions, whereas, surprisingly, increasing the coverage with catechol makes the non-dissociative mechanism the most stable one, revealing possible coexistence of a dissociative and non-dissociative anchoring at high coverage. This work unraveled a variety of adsorption fashions of the diol compounds in conjunction with the impact of the coverage effect, highly dependent on the nature of the lateral chain of the anchor group.

Communication: Singularity-free hybrid functional with a Gaussian-attenuating exact exchange in a plane-wave basis.

Integrable singularity in the exact exchange calculations in hybrid functionals is an old and well-known problem in plane-wave basis. Recently, we developed a hybrid functional named Gaussian-attenuating Perdew-Burke-Ernzerhof (Gau-PBE), which uses a Gaussian function as a modified Coulomb potential for the exact exchange. We found that the modified Coulomb potential of Gaussian function enables the exact exchange calculation in plane-wave basis to be singularity-free and, as a result, the Gau-PBE functional shows faster energy convergence on k and q grids for the exact exchange calculations. Also, a tight comparison (same k and q meshes) between Gau-PBE and two other hybrid functionals, i.e., PBE0 and HSE06, indicates Gau-PBE functional as the least computational time consuming. The Gau-PBE functional employed in conjunction with a plane wave basis provides bandgaps with higher accuracy than the PBE0 and HSE06 in agreement with bandgaps previously calculated using Gaussian-type-orbitals.

Study of Optoelectronic Features in Polar and Nonpolar Polymorphs of the Oxynitride Tin-Based Semiconductor InSnO2N.

In view of its potential applicability in photoconversion processes, we here discuss the optoelectronic features of the recently proposed tin-based oxynitride material for (photo)catalysis, InSnO2N. In detail, by combining Density Functional and Many-Body Perturbation Theory, we compute the electronic and optical properties discussing how they vary from the nonpolar phase to the more stable polar one. After providing a detailed, unbiased, description of the optoelectronic features of the two phases, we have finally calculated the Spectroscopic Limited Maximum Efficiency and obtained data that further witness the relevance of InSnO2N for solar energy conversion processes.

Chirality Effects and Semiconductor versus Metallic Nature in Halide Nanotubes.

A density functional theory study of the electronic structure of nanostructures based on the hexagonal layers of LuI3 is reported. Both bulk and slabs with one to three layers exhibit large and indirect bandgaps. Different families of nanotubes can be generated from these layers. Semiconducting nanotubes of two different chiralities have been studied. The direct or indirect nature of the optical gaps depends on the chirality, and a simple rationalization of this observation based on band folding arguments is provided. Remarkably, a metastable form of the armchair LuI3 nanotubes can be obtained under a structural rearrangement such that some iodine atoms are segregated toward the center of the nanotube forming chains of dimerized iodines. These nanotubes having an Lu2N I5N backbone are predicted to be metallic and should be immune toward a Peierls distortion. The iodine chains in the inner part of the nanotubes are weakly bound to the backbone so that it should be possible to remove these chains to generate a new series of neutral Lu2N I5N nanotubes which could exhibit interesting magnetic behavior. Because the LuI3 structure occurs for a large number of lanthanide and actinide trihalides, a tuning of the optical, transport, and probably magnetic properties of these new families of nanotubes can be a challenging prospect for future experimental studies.

Tailoring High-Entropy Oxides as Emerging Radiative Materials for Daytime Passive Cooling.

In the framework of intense research about high-entropy materials and their applications in energy-oriented technologies, in the present work, we discuss the potential applicability of selected oxides and of the alloys they form at different concentrations for daytime radiative cooling implementation. In particular, by combining density functional theory and the finite difference method, we provide an unbiased, scattering-free description of structural, electronic, and dynamic features of the best candidates, showing the required strong radiative properties for passive cooling while offering the benefits of affordability and compatibility with commercial coating fabrication processes.

Plurality of excitons in Ruddlesden-Popper metal halides and the role of the B-site metal cation.

We investigate the effect of metal cation substition on the excitonic structure and dynamics in a prototypical Ruddlesden-Popper metal halide. Through an in-depth spectroscopic and theoretical analysis, we identify the presence of multiple resonances in the optical spectra of a phenethyl ammonium tin iodide, a tin-based RPMH. Based on ab initio calculations, we assign these resonances to distinct exciton series that originate from the splitting of the conduction band due to spin-orbit coupling. While the splitting energy in the tin based system is low enough to enable the observation of the higher lying exciton in the visible-range spectrum of the material, the higher splitting energy in the lead counterpart prevents the emergence of such a feature. We elucidate the critical role played by the higher lying excitonic state in the ultrafast carrier thermalization dynamics.

Ab Initio Study of Graphene/hBN Van der Waals Heterostructures: Effect of Electric Field, Twist Angles and p-n Doping on the Electronic Properties.

In this work, we study the structural and electronic properties of boron nitride bilayers sandwiched between graphene sheets. Different stacking, twist angles, doping, as well as an applied external gate voltage, are reported to induce important changes in the electronic band structure near the Fermi level. Small electronic lateral gaps of the order of few meV can appear near the Dirac points K. We further discuss how the bandstructures change applying a perpendicular external electric field, showing how its application lifts the degeneracy of the Dirac cones and, in the twisted case, moves their crossing points away from the Fermi energy. Then, we consider the possibility of co-doping, in an asymmetric way, the two external graphene layers. This is a situation that could be realized in heterostructures deposited on a substrate. We show that the co-doping acts as an effective external electric field, breaking the Dirac cones degeneracy. Finally, our work demonstrates how, by playing with field strength and p-n co-doping, it is possible to tune the small lateral gaps, pointing towards a possible application of C/BN sandwich structures as nano-optical terahertz devices.

Bidimensional Engineered Amorphous a-SnO2 Interfaces: Synthesis and Gas Sensing Response to H2S and Humidity.

Two-dimensional (2D) transition metal dichalcogenides (TMDs) and metal chalcogenides (MCs), despite their excellent gas sensing properties, are subjected to spontaneous oxidation in ambient air, negatively affecting the sensor's signal reproducibility in the long run. Taking advantage of spontaneous oxidation, we synthesized fully amorphous a-SnO2 2D flakes (≈30 nm thick) by annealing in air 2D SnSe2 for two weeks at temperatures below the crystallization temperature of SnO2 (T < 280 °C). These engineered a-SnO2 interfaces, preserving all the precursor's 2D surface-to-volume features, are stable in dry/wet air up to 250 °C, with excellent baseline and sensor's signal reproducibility to H2S (400 ppb to 1.5 ppm) and humidity (10-80% relative humidity (RH)) at 100 °C for one year. Specifically, by combined density functional theory and ab initio molecular dynamics, we demonstrated that H2S and H2O compete by dissociative chemisorption over the same a-SnO2 adsorption sites, disclosing the humidity cross-response to H2S sensing. Tests confirmed that humidity decreases the baseline resistance, hampers the H2S sensor's signal (i.e., relative response (RR) = Ra/Rg), and increases the limit of detection (LOD). At 1 ppm, the H2S sensor's signal decreases from an RR of 2.4 ± 0.1 at 0% RH to 1.9 ± 0.1 at 80% RH, while the LOD increases from 210 to 380 ppb. Utilizing a suitable thermal treatment, here, we report an amorphization procedure that can be easily extended to a large variety of TMDs and MCs, opening extraordinary applications for 2D layered amorphous metal oxide gas sensors.

Materials Design and Optimization for Next-Generation Solar Cell and Light-Emitting Technologies.

We review some of the most potent directions in the design of materials for next-generation solar cell and light-emitting technologies that go beyond traditional solid-state inorganic semiconductor-based devices, from both the experimental and computational standpoints. We focus on selected recent conceptual advances in tackling issues which are expected to significantly impact applied literature in the coming years. Specifically, we consider solution processability, design of dopant-free charge transport materials, two-dimensional conjugated polymeric semiconductors, and colloidal quantum dot assemblies in the fields of experimental synthesis, characterization, and device fabrication. Key modeling issues that we consider are calculations of optical properties and of effects of aggregation, including recent advances in methods beyond linear-response time-dependent density functional theory and recent insights into the effects of correlation when going beyond the single-particle ansatz as well as in the context of modeling of thermally activated fluorescence.

Carbon Nanotubes/Regenerated Silk Composite as a Three-Dimensional Printable Bio-Adhesive Ink with Self-Powering Properties.

In this study, regenerated silk (RS) obtained from Bombyx Mori cocoons is compounded with carboxyl-functionalized carbon nanotubes (f-CNTs) in an aqueous environment for the fabrication of functional bio-adhesives. Molecular interactions between RS and carboxyl groups of CNTs result in structural increase of the ß-sheet formation, obtaining a resistant adhesive suitable for a wet biological substrate. Moreover, the functionalization of CNTs promotes their dispersion in RS, thus enabling the production of films with controlled electrical conductivity. The practical utility of such a property is demonstrated through the fabrication of a piezoelectric device implanted in a rat to monitor the breathing in vivo and to be used as a self-powered system. Finally, RS/f-CNTs were used as a printable biomaterial ink to three dimensionally print bilayer hollow tubular structures composed of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and RS. Initial tests carried out by seeding and growing human skin fibroblasts demonstrated that the 3D printed bilayer hollow cylindrical structures offer a suitable surface for the seeded cells to attach and proliferate. In general, the herein proposed RS/f-CNT composite serves as a versatile material for solvent-free dispersion processing and 3D printing, thus paving a new approach to prepare multifunctional materials with potential applications of great interest in sealing biological substrates and implantable devices for regenerative medicine.