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Charge-displacement (CD) analysis has recently proven to be a simple and powerful scheme for quantitatively analyzing the profile the charge redistribution occurring upon intermolecular interactions along a given interaction axis. However, when two molecular fragments bind through complex interactions involving multiple concurrent charge flows, ordinary CD analysis is capable of providing only an averaged picture of the related charge-flow profiles and no detailed information on each of them. In this article, we combine CD analysis with a Hirshfeld partitioning of the molecular charge redistribution for a local analysis on focused portions of the molecule, allowing for a detailed characterization of one charge flow at a time. The resulting scheme—the local charge-displacement (LCD) analysis—is tested on the intriguing case of the dimethyl sulfide–sulfur dioxide complex, characterized by concurrent charge flows relating to a sulfur–sulfur homochalcogen interaction and a pair of hydrogen bonds. The LCD scheme is then applied to the analysis of multiple hydrogen bonding in the acetic acid dimer, of base-pairing interactions in DNA, and of ambifunctional hydrogen bonding in the ammonia–pyridine complex. [ABSTRACT FROM AUTHOR]

Antimony selenide (Sb2Se3) is today one of the most promising alternative materials for p-type absorbers in thin-film photovoltaics, with an optimal band-gap and a very high absorption coefficient. However, its crystal structure is extremely anisotropic and its natural carrier density is generally very low. Sb2Se3 thin films have been deposited by two different high-energy techniques: magnetron RF-sputtering (MS) and low-temperature pulsed electron deposition (LT-PED). Their dominant crystallographic orientations have been studied as a function of deposition parameters and of the different used substrates, while complete solar cells have been subsequently made with the obtained samples to confirm the dependence of conversion efficiencies on the observed (Sb4Se6)n ribbon orientation. Cu-doped Sb2Se3 thin-films have been also preliminary prepared in order to evaluate a possible route to further improve the free charge-carrier density and the cell performance.

We report on the room temperature, simple and cheap preparation by mechano-synthesis of polycrystalline targets of complex sulphide semiconductors, namely CuInS2 (CIS), to be used for film deposition in physical vacuum techniques such as PLD, sputtering or LT-PED. The sulphur (S)-based targets usually require expensive high pressure equipment to compensate the high S vapour pressure; nevertheless they are indispensable for the deposition of high band-gap semiconductor materials. The comparison of CIS films grown by mechano-synthesis and by commercial targets demonstrates similar material quality, making the mechano-synthesis a viable solution in the fabrication of high band-gap, S-based targets of complex chalcogenides. [ABSTRACT FROM AUTHOR]

We carry out quasi-classical trajectory calculations for the C + CH+→ C+2 + H reaction on an ad hoc computed high-level ab initio potential energy surface. Thermal rate coefficients at the temperatures of relevance in cold interstellar clouds are derived and compared with the assumed, temperature-independent estimates publicly available in kinetic data bases KIDA and UDfA. For a temperature of 10 K the data base value overestimates by a factor of 2 the one obtained by us (thus improperly enhancing the destruction route of CH+ in astrochemical kinetic models) which is seen to double in the temperature range 5-300 K with a sharp increase in the first 50 K. The computed values are fitted via the popular Arrhenius-Kooij formula and best-fitting parameters α = 1.32 ? 10-9 cm³ s-1, β = 0.1 and γ = 2.19 K to be included in the online mentioned data bases are provided. Further investigation shows that the temperature dependence of the thermal rate coefficient better conforms to the recently proposed so-called 'deformed Arrhenius' law by Aquilanti and Mundim. [ABSTRACT FROM AUTHOR]

We carry out quasi-classical trajectory calculations for the C + CH+→ C+2 + H reaction on an ad hoc computed high-level ab initio potential energy surface. Thermal rate coefficients at the temperatures of relevance in cold interstellar clouds are derived and compared with the assumed, temperature-independent estimates publicly available in kinetic data bases KIDA and UDfA. For a temperature of 10 K the data base value overestimates by a factor of 2 the one obtained by us (thus improperly enhancing the destruction route of CH+ in astrochemical kinetic models) which is seen to double in the temperature range 5-300 K with a sharp increase in the first 50 K. The computed values are fitted via the popular Arrhenius-Kooij formula and best-fitting parameters α = 1.32 ? 10-9 cm³ s-1, β = 0.1 and γ = 2.19 K to be included in the online mentioned data bases are provided. Further investigation shows that the temperature dependence of the thermal rate coefficient better conforms to the recently proposed so-called 'deformed Arrhenius' law by Aquilanti and Mundim. [ABSTRACT FROM AUTHOR]

We report on the development of an unconventional method for heating a Mo-coated substrate during the deposition of a Cu(In,Ga)Se2 (CIGS) layer by the pulsed electron deposition technique, to be used as absorber in thin film solar cells. This method is based on the application of a DC electrical power directly through the Mo back contact of the cell, converting electrical energy into heat by Joule effect. Since the current flows only on the superficial metal-coated region of the substrate, a localized heating of the surface can be achieved, thus limiting the heat losses. Due to the very efficient heat transfer to the thin Mo layer, a very little electrical power density (few W/cm²) is enough to achieve the required deposition temperature on the Mo surface, much lower compared to the traditional resistor- or lamp-based external heaters. The morphological and electrical properties of Joule-heated samples have been compared to those of CIGS films heated by a conventional external heater. As far as the structure concerns, a remarkable difference is revealed by Scanning Electron Microscopy analysis, indicating a significant enlargement of the CIGS grains size on Joule-heated samples. On the contrary, Capacitance-Voltage and Current-Voltage measurements evidence similar electrical features: both types of heated samples have a net free carrier concentration ≈5 x 1015cm-3, resulting in a similar photovoltaic conversion efficiency (≈15%). The main recombination path, deduced from the dependence of VOC on the temperature, results to be the Shockley-Read-Hall mechanism in both types of the absorber layer. These results indicate that the Joule effect could be adopted as a feasible, low cost alternative heating method for growing high quality CIGS layers. [ABSTRACT FROM AUTHOR]

Raman spectroscopy, a versatile and nondestructive technique, was employed to develop a methodology for gallium oxide (Ga 2 O 3 ) phase detection and identification. This methodology combines experimental results with a comprehensive literature survey. The established Raman approach offers a powerful tool for nondestructively assessing phase purity and detecting secondary phases in Ga 2 O 3 thin films. X-ray diffraction was used for comparison, highlighting the complementary information that these techniques may provide for Ga 2 O 3 characterization. Few case studies are included to demonstrate the usefulness of the proposed spectroscopic approach, namely the impact of deposition conditions such as metal-organic vapor-phase epitaxy and pulsed electron deposition (PED), and extrinsic elements provided during growth (Sn in the case of PED) on Ga 2 O 3 polymorphism. In conclusion, it is shown that Raman spectroscopy offers a quick, reliable, and nondestructive high-resolution approach for Ga 2 O 3 thin film characterization, especially concerning phase detection and crystalline quality., Competing Interests: Declaration of Conflicting InterestsThe authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Vinyl alcohol (VyA) and cyanide (CN) radicals are relatively abundant in the interstellar medium (ISM). VyA is the enolic tautomer of acetaldehyde and has two low-lying conformers, characterized by the syn or anti placement of hydroxyl hydrogen with respect to the double bond. In this paper, we present a gas-phase model of the barrierless reactions of both VyA's conformers with CN employing accurate quantum chemical computations in the framework of a master equation approach based on the transition state theory. Our results indicate that both VyA conformers feature a similar reactivity with CN, starting with a barrierless addition to the double bond and followed by different isomerization, dissociation, and/or hydrogen elimination steps. The rate constants computed for temperatures up to 600 K show that several reaction channels are open even under the harsh conditions of the ISM, with the favoured one providing the first feasible formation route of a prebiotic molecule not yet detected in the ISM, namely cyanoacetaldehyde. This finding suggests looking for cyanoacetaldehyde in regions where both VyA and CN have already been detected, like, e.g. , Sagittarius B2N or G+0.693-0.027.

Stochastic modeling approaches can be used to rationalize complex molecular dynamical behaviours in solution, helping to interpret the coupling mechanisms among internal and external degrees of freedom, providing insight into reaction mechanisms and extracting structural and dynamical data from spectroscopic observables. However, the definition of comprehensive models is usually limited by (i) the difficulty in defining - without resorting to phenomenological assumptions - a representative reduced ensemble of molecular coordinates able to capture essential dynamical properties and (ii) the complexity of numerical or approximate treatments of the resulting equations. In this paper, we address the first of these two issues. Building on a previously defined systematic approach to construct rigorous stochastic models of flexible molecules in solutions from basic principles, we define a manageable diffusive framework leading to a Smoluchowski equation determined by one main tensorial parameter, namely the scaled roto-conformational diffusion tensor, which accounts for the influence of both conservative and dissipative forces and describes the molecular mobility via a precise definition of internal-external and internal-internal couplings. We then show the usefulness of the roto-conformational scaled diffusion tensor as an efficient gauge of molecular flexibility through the analysis of a set of molecular systems of increasing complexity ranging from dimethylformamide to a protein domain.

Multiferroics, showing the coexistence of two or more ferroic orderings at room temperature, could harness a revolution in multifunctional devices. However, most of the multiferroic compounds known to date are not magnetically and electrically ordered at ambient conditions, so the discovery of new materials is pivotal to allow the development of the field. In this work, we show that BaFe 2 O 4 is a previously unrecognized room temperature multiferroic. X-ray and neutron diffraction allowed to reveal the polar crystal structure of the compound as well as its antiferromagnetic behavior, confirmed by bulk magnetometry characterizations. Piezo force microscopy and electrical measurements show the polarization to be switchable by the application of an external field, while symmetry analysis and calculations based on density functional theory reveal the improper nature of the ferroelectric component. Considering the present findings, we propose BaFe 2 O 4 as a Bi- and Pb-free model for the search of new advanced multiferroic materials., (© 2022. The Author(s).)

Copper-doped antimony selenide (Cu-doped Sb 2 Se 3 ) thin films were deposited as absorber layers in photovoltaic solar cells using the low-temperature pulsed electron deposition (LT-PED) technique, starting from Sb 2 Se 3 targets where part of the Sb was replaced with Cu. From a crystalline point of view, the best results were achieved for thin films with about Sb 1.75 Cu 0.25 Se 3 composition. In order to compare the results with those previously obtained on undoped thin films, Cu-doped Sb 2 Se 3 films were deposited both on Mo- and Fluorine-doped Tin Oxide (FTO) substrates, which have different influences on the film crystallization and grain orientation. From the current-voltage analysis it was determined that the introduction of Cu in the Sb 2 Se 3 absorber enhanced the open circuit voltage (V OC ) up to remarkable values higher than 500 mV, while the free carrier density became two orders of magnitude higher than in pure Sb 2 Se 3 -based solar cells.

The Charge-Displacement (CD) analysis has proven to be a powerful tool for a quantitative characterization of the electron-density flow occurring upon chemical bonding along a suitably chosen interaction axis. In several classes of interesting intermolecular interactions, however, an interaction axis cannot be straightforwardly defined, and the CD analysis loses consistency and usefulness. In this article, we propose a general, flexible reformulation of the CD analysis capable of providing a quantitative view of the charge displacement along custom curvilinear paths. The new scheme naturally reduces to ordinary CD analysis if the path is chosen to be a straight line. An implementation based on a discrete sampling of the electron densities and a Voronoi space partitioning is described and shown in action on two test cases of a metal-carbonyl and a pyridine-ammonia complex.

A framework for the stochastic description of relaxation processes in flexible macromolecules including dissipative effects has been recently introduced, starting from an atomistic view, describing the joint relaxation of internal coordinates and global degrees of freedom, and depending on parameters recoverable from classic force fields (energetics) and medium modelling at the continuum level (friction tensors). The new approach provides a rational context for the interpretation of magnetic resonance relaxation experiments. In its simplest formulation, the semi-flexible Brownian (SFB) model has been until now shown to reproduce correctly correlation functions and spectral densities related to orientational properties obtained by direct molecular dynamics simulations of peptides. Here, for the first time, we applied directly the SFB approach to the practical evaluation of high-quality 13 C nuclear magnetic resonance relaxation parameters, T1 and T2, and the heteronuclear NOE of several oligosaccharides, which were previously interpreted on the basis of refined ad hoc modelling. The calculated NMR relaxation parameters were in agreement with the experimental data, showing that this general approach can be applied to diverse classes of molecular systems, with the minimal usage of adjustable parameters.

Chemical bonding in a set of six cuprous complexes with simple nitriles (CN-, HNC, HCN, CH3NC, and CH3CN) is investigated by means of a recently devised analysis scheme framed in density-functional theory and quantitatively singling out concurrent charge flows such as σ donation and π backdonation. The results of our analysis are comparatively assessed against qualitative models for charge redistribution based on the popular concepts of octet rule and resonance structures, and the relative importance of different charge-flow channels relating to σ donation, π back-donation, polarization, and hyperconjugation is discussed on a quantitative basis.

We report on the high-pressure solid-state synthesis and the detailed structural characterization of the metastable, CuAu-type CuInS 2 (CA-CIS) phase. Although often present in CIS thin films as unwanted phase, it has been never synthesized in pure form, and its effect on the performance of CIS-based solar cells has been long debated. In this work, pure CA-CIS phase is synthesized in bulk polycrystalline form through a high-pressure-high-temperature solid-state reaction. Single-crystal X-rays diffraction reveals the formation of tetragonal CA-CIS ( a = 3.9324(5), c = 5.4980(7) Å) either in cation-ordered and disordered phase, pointing out the role of the pressure/temperature increase on the Cu/In ordering. The resistivity measurements performed on CA-CIS show low resistivity and a flat trend vs temperature and, in the case of the ordered phase, highlight a bad-metallic behavior, probably due to a high level of doping. These findings clearly rule out the possibility of a beneficial effect of this phase on the CIS-based thin film solar cells.

The virtual-reality framework AVATAR (Advanced Virtual Approach to Topological Analysis of Reactivity) for the immersive exploration of potential-energy landscapes is presented. AVATAR is based on modern consumer-grade virtual-reality technology and builds on two key concepts: (a) the reduction of the dimensionality of the potential-energy surface to two process-tailored, physically meaningful generalized coordinates, and (b) the analogy between the evolution of a chemical process and a pathway through valleys (potential wells) and mountain passes (saddle points) of the associated potential energy landscape. Examples including the discovery of competitive reaction paths in simple A + BC collisional systems and the interconversion between conformers in ring-puckering motions of flexible rings highlight the innovation potential that augmented and virtual reality convey for teaching, training, and supporting research in chemistry., (© 2020 Wiley Periodicals, Inc.)

We present a four-component relativistic density functional theory study of the chemical bond and s-d hybridization in the group 11 cyanides M-CN (M = Cu, Ag, and Au). The analysis is carried out within the charge-displacement/natural orbital for chemical valence (CD-NOCV) scheme, which allows us to single out meaningful contributions to the total charge rearrangement that arises upon bond formation and to quantify the components of the Dewar-Chatt-Duncanson bonding model (the ligand-to-metal donation and metal-to-ligand back-donation). The M-CN bond is characterized by a large donation from the cyanide ion to the metal cation and by two small back-donation components from the metal toward the cyanide anion. The case of gold cyanide elucidates the peculiar role of the relativistic effects in determining the characteristics of the Au-C bond with respect to the copper and silver homologues. In AuCN, the donation and back-donation components are significantly enhanced, and the spin-orbit coupling, removing the degeneracy of the 5d atomic orbitals, induces a substantial split in the back-donation components. A simple spatial analysis of the NOCV-pair density, related to the ligand-to-metal donation component, allows us to quantify, with unprecedented accuracy, the charge rearrangement due to the s-d hybridization occurring at the metal site. The s-d hybridization plays a key role in determining the shape and size of the metal; it removes electron density from the bond axis and induces a significant flattening at the metal site in the position trans to the ligand. The s-d hybridization is present in all noble metal complexes, influencing the bond distances, and its effect is enhanced for Au, which is consistent with the preference of gold to form linear complexes. A comparative investigation of simple complexes [AuL] +/0 of Au + with different ligands (L = F - , N -heterocyclic carbene, CO, and PH 3 ) shows that the s-d hybridization mechanism is also influenced by the nature of the ligand.

Ring-puckering motion in 12 flexible cyclic molecules is investigated by calculation and analysis of two-dimensional potential-energy surfaces (PESs) using the so-called ring-puckering coordinates proposed by Cremer and Pople. The PESs are calculated by means of density-functional theory using a B2PLYP-D3BJ exchange-correlation functional with a maug-cc-pVTZ basis set, and results are compared to the available experimental and theoretical data. Special care is devoted to the aspect of symmetry in such two-dimensional PESs, which are here reported for the first time also for molecules whose planar form has symmetry lower than D 5 h or C 2 v . The issue of PES fitting and that of solving the nuclear dynamics using ring-puckering coordinates are also addressed. Analytical formulations of the computed PESs using suitable functional forms with a limited set of parameters are provided.

Circular dichroism spectra in the IR range (VCD = vibrational circular dichroism) and in the UV range (ECD = electronic circular dichroism) have been recorded for both enantiomers of simple mono-substituted ferrocenes containing chiral pendants: 1-acetoxyethylferrocene, 1, 1-methoxyethylferrocene, 2, and 1-hydroxyethylferrocene, 3; the related disubstituted 1,1'-bis(1-hydroxyethyl)ferrocene, 4, was also considered. These two types of spectra, with the support of DFT calculations, concur to unequivocally confirm the absolute configuration for 1-4. In particular, our computational results point out the clear advantage of using an anharmonic oscillator model for the interpretation of VCD spectra of chiral ferrocenes. Interesting conformational properties are either confirmed or established by the technique, like the eclipsed conformation of the two cyclopentadienyl rings and an intra-molecular interaction involving the OH for 3. For 4, NMR, VCD and IR spectra are compatible with dimer formation and in this case a distorted conformation is predicted. Of utmost importance for the absolute configuration assignment in mono-substituted ferrocenes, we were able to identify a diagnostic VCD band at 950 cm-1 and a (low intensity) ECD band that clearly indicate the absolute configuration of the whole series.

By combining rotational spectroscopy in supersonic expansion with the capability of state-of-the-art quantum-chemical computations in accurately determining structural and energetic properties, the genuine nature of a sulfur-sulfur chalcogen bond between dimethyl sulfide and sulfur dioxide has been unveiled in a gas-jet environment free from collision, solvent and matrix perturbations. A SAPT analysis pointed out that electrostatic S⋅⋅⋅S interactions play the dominant role in determining the stability of the complex, largely overcoming dispersion and C-H⋅⋅⋅O hydrogen-bond contributions. Indeed, in agreement with the analysis of the quadrupole-coupling constants and of the methyl internal rotation barrier, the NBO and NOCV/CD approaches show a marked charge transfer between the sulfur atoms. Based on the assignment of the rotational spectra for 7 isotopologues, an accurate semi-experimental equilibrium structure for the heavy-atom backbone of the molecular complex has been determined, which is characterized by a S⋅⋅⋅S distance (2.947(3) Å) well below the sum of van der Waals radii., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A gas-phase nitrogen-nitrogen noncovalent interaction has been unveiled in the nitroethane-trimethylamine complex in an environment free from solvent and matrix effects using rotational spectroscopy in supersonic expansion. Different quantum chemical models (NOCV/CD and NBO) agree in indicating that this interaction largely prevails over the C-H⋅⋅⋅O and C-H⋅⋅⋅N hydrogen bonds. Furthermore, a SAPT analysis shows that electrostatic and dispersion interactions play a comparable role in stabilizing the complex. The conformational landscape exploration and stationary points characterization have been performed using state-of-the-art quantum-chemical computations providing significant insights on structure determination., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

We have recently introduced a simple yet powerful tool for analyzing quantitatively the coordination bond in terms of the donation and back-donation constituents of the Dewar-Chatt-Duncanson model. Our approach is based on the decomposition, via natural orbitals for chemical valence (NOCV), of the so-called charge-displacement (CD) function into additive chemically meaningful components (Bistoni et al. J. Chem. Phys. 2015, 142, 084112 ). The method, referred to as NOCV/CD, provides clear-cut measures of donation and back-donation charge flows following bond formation, and its robustness has been demonstrated by a tight correlation of the related charge-transfer estimates with experimental observables. In this paper we extend the NOCV/CD analysis scheme to the four-component relativistic framework, which includes spin-orbit coupling variationally. This formalism is incorporated into a recently developed, highly efficient parallel version of the relativistic Dirac-Kohn-Sham (DKS) program BERTHA (Rampino et al. J. Chem. Theory Comput. 2014, 10, 3766-3776 ). We test the accuracy and numerical stability of this new implementation through the analysis of the convergence properties of the basis sets employed to expand the DKS spinor solution and those used to linearize the electronic density in the density-fitting algorithm speeding up the evaluation of the DKS matrix. An illustration of NOCV/CD analysis in the relativistic framework is also given through a study of the metal-carbonyl coordination bond in a series of [M-CO] + (M = Cu, Ag, Au) complexes of group 11 metals, where relativistic effects, including spin-orbit coupling, are found to play an important role.

Through an analysis of eighty tetrahedral and square-planar metal carbonyls of general formula [M(CO)(L')(L) 2 ] including newly synthesized chlorocarbonyl rhodium complexes with chelating atropoisomeric diphosphanes, we show how coordination geometry can switch the carbonyl stretching frequency into a selective probe of the σ-donor and π-acceptor abilities of the ligands. We thus provide a framework whereby the σ-donation and π-backdonation constituents of the Dewar-Chatt-Duncanson model can be quantitatively predicted through spectroscopic data on coordinated CO moieties and vice versa.

The relation between spectroscopic observables and the detailed metal-ligand bonding features in chelation complexes is addressed using both experimental and state-of-the-art theoretical and computational methods. We synthesized and characterized a set of six nickel dicarbonyl complexes of general formula [Ni(CO) 2 (PP)], where PP is an atropoisomeric chelating diphosphine ligand. The analysis of the obtained experimental data and the basicity and oxidative potentials of the free ligands suggests a close relation between the donor ability of the chelating ligand and the carbonyl stretching frequencies observed in the complexes. We then use theory to unravel the detailed mechanisms of chelation-bond formation in terms of partial charge flows between the molecular orbitals of the fragments. By extending the promising, recently published natural orbitals for chemical valence/charge displacement (NOCV/CD) analysis scheme we provide a thorough, quantitative description of the several charge fluxes following the metal-ligand bond formation and demonstrate that the carbonyl stretching frequencies in the considered complexes selectively respond to the σ-donation charge flow from the phosphorus lone pairs of the ligands, with the frequency shift being in quantitative correlation with the extent of the ligand-to-metal charge transfer.