Favorable Configuration Research Articles

Efficient photocatalytic overall water splitting for hydrogen evolution and CO2 reduction with SiCP4 allotrope monolayers

Two-dimensional metal-free photocatalysts are catching the attention of researchers. Here, we present several allotrope SiCP4 monolayers with high stability, high carrier mobility, and excellent photocatalytic performance. Using a searching method based on the universal structure predictor evolutionary xtallography, together with assessing the energy and thermodynamic stabilities, and matching the potentials of band edges with the photocatalytic conditions for achieving overall water splitting, we successfully identify 5 highly favorable configurations (including the previously reported one) from a pool of 1056 allotrope SiCP4 monolayers. The results show that the largest solar-to-hydrogen efficiency of the considered monolayers can reach 21.89 %, while a high mobility of 2.7677 × 105 cm2 V−1 s−1 is observed, both are superior to those of the previously reported one. The Gibbs free energies for hydrogen or oxygen evolutions, and CO2 reduction reactions indicate they are thermodynamically feasible. Moreover, the hydrogen evolution reaction can proceed spontaneously with two allotrope SiCP4 monolayers. Therefore, the newfound allotrope SiCP4 monolayers are expected to have potential applications in the field of photocatalytic water splitting for hydrogen generation and carbon dioxide reduction.

An improved algorithm of generating shortening patterns for polar codes

The rate matching in polar codes becomes a solution when non-conventional codewords of length N≠2n are required. Shortening is employed to design arbitrary rate codes from a mother code with a given rate. Based on the conventional shortening scheme, length of constructed polar codes is limited. In this paper, we demonstrate the presence of favorable and unfavorable shortening patterns. The structure of polar codes is leveraged to eliminate unfavorable shortening patterns, thereby reducing the search space. We generate an auxiliary matrix through likelihood and subsequently select the shortening bits from the matrix. Unlike different existing methods that offer only a single shortening pattern, our algorithm generates multiple favorable shortening patterns, encompassing all possible favorable configurations. This algorithm has a reduced complexity and suboptimal performance, effectively identifying shortening patterns and sets of frozen symbols for any polar code. Simulation results underscore that the shortened polar codes exhibit performance closely aligned with the mother codes. Our algorithm addresses this security concern by making it more difficult for an attacker to obtain the information set and frozen symbols of a polar code. This is done by generating multiple shortening patterns for any polar code.

Assessing mutualistic metacommunity capacity by integrating spatial and interaction networks

We develop a spatially realistic model of mutualistic metacommunities that exploits the joint structure of spatial and interaction networks. Assuming that all species have the same colonisation and extinction parameters, this model exhibits a sharp transition between stable non-null equilibrium states and a global extinction state. This behaviour allows defining a threshold on colonisation/extinction parameters for the long-term metacommunity persistence. This threshold, the ‘metacommunity capacity’, extends the metapopulation capacity concept and can be calculated from the spatial and interaction networks without needing to simulate the whole dynamics. In several applications we illustrate how the joint structure of the spatial and the interaction networks affects metacommunity capacity. It results that a weakly modular spatial network and a power-law degree distribution of the interaction network provide the most favourable configuration for the long-term persistence of a mutualistic metacommunity. Our model that encodes several explicit ecological assumptions should pave the way for a larger exploration of spatially realistic metacommunity models involving multiple interaction types.

Binuclear methylphosphinidine complexes of cyclopentadienylruthenium carbonyls: effects of the higher ligand field strength of ruthenium derivatives relative to iron derivatives.

The structures and energetics of the binuclear methylphosphinidene complexes of cyclopentadienylruthenium carbonyls of the type [MePRu2(CO)nCp2] (n = 4, 3, 2, 1) have been investigated for comparison with their previously studied iron analogues. For the tetracarbonyls and tricarbonyls [MePM2(CO)nCp2] (n = 4, 3) substituting ruthenium for iron has relatively little effect on the energetically preferred structures. Thus such structures have two-electron donor bridging MeP groups with no metal-metal bond for the tetracarbonyls and a metal-metal single bond for the tricarbonyls. This leads to favored 18-electron configurations for both ruthenium atoms in all cases. However, the higher ligand field strengths of ruthenium complexes relative to analogous iron complexes have major effects on the energetically preferred structures for the dicarbonyls and monocarbonyls [MePM2(CO)nCp2] (M = Fe, Ru; n = 2, 1). Thus the 11 lowest energy structures for the dicarbonyl [MePFe2(CO)2Cp2] are triplet or quintet spin state structures whereas the 6 lowest energy structures for the ruthenium analogue [MePRu2(CO)2Cp2] are all singlet structures. These low-energy singlet [MePRu2(CO)2Cp2] structures include species in which both ruthenium atoms attain the favored 18-electron configurations in different ways: either by a Ru-Ru single bond and an agostic C-H-Ru interaction from the methyl group, a Ru-Ru single bond and a four-electron donor bridging MeP ligand with PRu double bonds, or a formal RuRu double bond with a two-electron donor bridging MeP ligand. The 8 lowest energy structures for the diiron monocarbonyl [MePFe2(CO)Cp2] are all triplet or quintet spin structures whereas the lowest energy structure for the diruthenium monocarbonyl [MePRu2(CO)Cp2] by more than 20 kcal mol-1 is a singlet structure with a formal RuRu double bond and bridging CO and four-electron donor MeP groups. Thermochemical information predicts such monocarbonyl derivatives to be the dominant binuclear decarbonylation products of the tricarbonyls [RPRu2(CO)3Cp2] by thermal or photochemical methods.

ИССЛЕДОВАНИЕ ФИЗИКО-МЕХАНИЧЕСКИХ СВОЙСТВ ПОЛИУРЕТАНОВЫХ КОМПАУНДОВ ДЛЯ ОЦЕНКИ ВОЗМОЖНОСТИ ИХ ПРИМЕНЕНИЯ В МЕМБРАННО-ПОРШНЕВОМ НАСОСЕ

The diaphragms in diaphragm piston pumps serve as the main working parts, the failure of which entails the shutdown of the entire pump, and, as a result, the sprayer, which leads to a decrease in the efficiency of agricultural activities and an increase in the cost of restoring the operability of agricultural equipment. The relevance of using the technology of free casting of twocomponent polyurethane in silicone molds in the organization of repair sites is due to the high quality of the parts obtained with a significant reduction in cost, as well as production time. Since the main reason for the failure of the membrane is abrasive wear and cyclic loads, the determining properties are hardness, strength and ductility of the materials used. (Research purpose) The research purpose is assessing the hardness, strength and plasticity of polyurethane compounds of various brands, depending on the production conditions of the sample, and concluding their applicability to manufacture piston pump diaphragms by free casting. (Materials and methods) Presented studies of hardness, tensile strength and elongation at break of three grades of polyurethane compounds PolyFlex 80A, Advaform Mark 80 and Silagerm 6080, depending on the technological modes of manufacturing samples from them. (Results and discussion) It was found that the curing of polyurethane compounds at higher temperatures allows for high strength and plastic properties of the material. It was noted that during curing, molecules are redistributed into the most favorable energy configurations, which exclude the appearance of structural stress concentrators, increasing the plasticity and strength of the material. The increased temperature helps to remove residual stresses in the material that occur during shrinkage. (Conclusions) The application scope of the research results is the manufacture of polymer parts of agricultural machinery, in particular, diaphragm diaphragm piston pump.

Ligand-free 99mTc-polyurea dendrimer complexes: nanoradiotheranostics targeting ovarian cancer.

A folic acid-targeted polyurea (PURE) dendrimer was easily radiolabelled with Technetium-99m (99mTc-PUREG4-FA2) avoiding the use of additional ligands and bioconjugation chemistry. This straightforward strategy is enabled in PURE dendrimers due to their favourable surface terminal groups configuration, showing coordination capabilities and turning these biodendrimers into attractive platforms for nanoradiotheranostics.

Organic cations promote exciton dissociation in Ruddlesden-Popper lead iodide perovskites: a theoretical study.

Two-dimensional (2D) Ruddlesden-Popper perovskites (RPPs) are a class of quantum well (QW) materials showing large exciton binding energy owing to quantum confinement. The existence of localized edge states was proposed to accelerate exciton dissociation into long-lived charge carriers in 2D RPPs, but recent experimental reports suggested that highly efficient internal exciton dissociation is achievable in 2D RPPs despite the absence of edge states. Herein, we adopt first-principles calculations to unveil the physical origin of the high internal quantum efficiency in the bulk region of widely familiar (BA)2(MA)n-1PbnI3n+1 (BA = butylammonium; MA = methylammonium) materials. We discover that the dipolar nature of MA cations provides the driving force for the separation of photoexcited electron-hole pairs inside QWs as the inorganic layer thickens from n = 1 to n = 3. Concurrently, electronic coupling between organic spacer layers and QWs is enhanced in the energetically favorable configurations where MA cations orient with their CH3 groups towards the exterior PbI2 layers of QWs in the n = 3 structure. Consequently, hole delocalization is promoted along the out-of-plane direction of QWs, which in turn facilitates exciton dissociation into free charge carriers despite large exciton binding energy. Our simulations reveal that the hydrogen bonding between organic species (including both MA and BA cations) and iodine atoms, which is subtly interconnected, engineers the response of morphology in QWs and electronic interactions at organic-inorganic interfaces, providing novel insights for the exciton-free carrier behavior in the bulk area of 2D RPPs.

Nonadditivity in interactions between three membrane-wrapped colloidal spheres

Many cell functions require a concerted effort from multiple membrane proteins, for example, for signaling, cell division, and endocytosis. One contribution to their successful self-organization stems from the membrane deformations that these proteins induce. While the pairwise interaction potential of two membrane-deforming spheres has recently been measured, membrane-deformation-induced interactions have been predicted to be nonadditive, and hence their collective behavior cannot be deduced from this measurement. We here employ a colloidal model system consisting of adhesive spheres and giant unilamellar vesicles to test these predictions by measuring the interaction potential of the simplest case of three membrane-deforming, spherical particles. We quantify their interactions and arrangements and, for the first time, experimentally confirm and quantify the nonadditive nature of membrane-deformation-induced interactions. We furthermore conclude that there exist two favorable configurations on the membrane: (1) a linear and (2) a triangular arrangement of the three spheres. Using Monte Carlo simulations, we corroborate the experimentally observed energy minima and identify a lowering of the membrane deformation as the cause for the observed configurations. The high symmetry of the preferred arrangements for three particles suggests that arrangements of many membrane-deforming objects might follow simple rules.

Hydrogen-Bonded Supramolecular Nanotrap Enabling the Interfacial Activation of Hosted Enzymes.

Engineering nanotraps to immobilize fragile enzymes provides new insights into designing stable and sustainable biocatalysts. However, the trade-off between activity and stability remains a long-standing challenge due to the inevitable diffusion barrier set up by nanocarriers. Herein, we report a synergetic interfacial activation strategy by virtue of hydrogen-bonded supramolecular encapsulation. The pore wall of the nanotrap, in which the enzyme is encapsulated, is modified with methyl struts in an atomically precise position. This well-designed supramolecular pore results in a synergism of hydrogen-bonded and hydrophobic interactions with the hosted enzyme, and it can modulate the catalytic center of the enzyme into a favorable configuration with high substrate accessibility and binding capability, which shows up to a 4.4-fold reaction rate and 4.9-fold conversion enhancements compared to free enzymes. This work sheds new light on the interfacial activation of enzymes using supramolecular engineering and also showcases the feasibility of interfacial assembly to access hierarchical biocatalysts featuring high activity and stability simultaneously.

MXene heterostructures based on Cr2C and Cr2N: evidence of strong interfacial interactions that induce an antiferromagnetic alignment

In the present work, Cr2C and Cr2N MXenes are stacked to conform 2D heterostructures. The structural, electronic, and magnetic properties were further investigated. Two stackings were treated; the first, Cr2C on top of Cr2N, and the second, Cr2N is on Cr2C. The most favorable configuration is Cr2C/Cr2N, with a vertical distance of 2.35 Å. The antiferromagnetic alignment evidences a possible bias exchange effect. Cr2C MXene preserves its ferromagnetic behavior and changes the top Cr layer polarization of Cr2N form the antiferromagnetic alignment with Cr2C. The bottom Cr layer of Cr2N conserves the intrinsic polarization as antiparallel. Electronic properties evidence a metallic behavior. Although the vertical distance in the MXene heterostructure is comparable with a van der Waals interaction, the 2D charge density maps and electron local function indicate a metallic interaction at the interface, meanwhile the charge density difference exhibits a charge transfer in the interface heterostructure. The new 2D heterostructure and the properties that emerge from it could be interesting to the spintronics community due to their applications in information storage devices.

In silico investigation on sensing of tyramine by boron and silicon doped C60 fullerenes

The present communication deals with the adsorption of tyramine neurotransmitter over the surface of pristine, Boron (B) and Silicon (Si) doped fullerenes. Density functional theory (DFT) calculations have been used to investigate tyramine adsorption on the surface of fullerenes in terms of stability, shape, work function, electronic characteristics, and density of state spectra. The most favourable adsorption configurations for tyramine have been computed to have adsorption energies of − 1.486, − 30.889, and − 31.166 kcal/mol, respectively whereas for the rest three configurations, it has been computed to be − 0.991, − 6.999, and − 8.796 kcal/mol, respectively. The band gaps for all six configurations are computed to be 2.68, 2.67, 2.06, 2.17, 2.07, and 2.14 eV, respectively. The band gap of pristine, B and Si doped fullerenes shows changes in their band gaps after adsorption of tyramine neurotransmitters. However, the change in band gaps reveals more in B doped fullerene rather than pristine and Si doped fullerenes. The change in band gaps of B and Si doped fullerenes leads a change in the electrical conductivity which helps to detect tyramine. Furthermore, natural bond orbital (NBO) computations demonstrated a net charge transfer of 0.006, 0.394, and 0.257e from tynamine to pristine, B and Si doped fullerenes.

Variation of structured laser beam pattern and optimization for an alignment reference line creation.

The alignment of particle accelerators demands a dedicated measurement system based on a straight-line reference. This straight line can be provided by a laser beam. The alignment then involves accurately measuring the offset of accelerator components with respect to this light path. In order to be efficient, the laser beam needs to serve as a stable and straight reference for distances of several hundreds of meters. The attainable accuracy depends, among other parameters, on the laser spot size, which should ideally change very little over the distances at which the alignment system needs to operate. Due to the significant divergence of Gaussian laser beams, we propose using a structured laser beam (SLB) for alignment. Its transversal intensity profile is similar to a Bessel beam and consists of an intense inner core (IC) and concentric rings. The divergence of the IC, i.e., the growth of its size with distance, can be limited to 10μrad using a favorable generator configuration. Thus an SLB may be suitable as a straight-line reference for long-distance alignment applications. However, the SLB is distorted if obstructions cover parts of the outermost ring (OR) of the beam within, which should therefore also be small. In this paper, we investigate the relationship between the size of the IC and OR depending on the design parameters of the SLB generator. We use numerical simulations and experiments with different generators over distances up to 50 m to analyze the transversal intensity profile and wavefronts of different SLBs. The results indicate the general suitability of an SLB as a reference line for long-distance alignment but also expose tradeoffs between small IC and small OR. The findings outlined in the paper help to describe the optimal SLB parameters for given conditions.

Self-Constructing 100% Water-Resistant Metal Sulfides through In Situ Acid Etching for Effective Elemental Mercury (Hg0) Capture.

Metal sulfides (MSs) can efficiently entrap thiophilic components, such as elemental mercury (Hg0), and realize environmental remediation. However, there is still a critical problem challenging the extensive application of MSs in related areas, i.e., how to self-regulate their water (H2O) resistance without complexing the sorbent preparation procedure. This work for the first time developed an in situ acid-etching method that self-engineered the water affinity of MSs through changing the interfacial interaction between MSs and Hg0/H2O. The introduction of abundant, undercoordinated sulfur onto the sorbent surface was the primary reason accounting for the significantly improved H2O resistance. The high surface coverage of undercoordinated sulfur induced the formation of polysulfur chains (Sx2-) that stabilized Hg0 via a bridging bond and repelled H2O, attributed to the favorable electron configurations. These properties made the surface of MSs highly hydrophobic and increased the adsorption selectivity toward Hg0 over H2O. The MSs exhibited 100% H2O resistance even in the presence of 20% H2O, which is much higher than the H2O concentration under most practical scenarios. From these perspectives, this work for the first time overcame the detrimental effects of H2O on MSs through a self-regulating way that is scalable and negligibly complexes the sorbent preparation pathway. The highly water-resistant and cost-effective MSs as prepared can serve as efficient Hg0 removal from industrial flue gas in the future.

High Coordination Numbers of Actinides (An) in AnC13+ Rings (An = Th and U).

An intriguingly high abundance of both ThC13+ and UC13+ cluster cations was observed in a previous mass spectrometry experiment; however, the structural identification of these cations has not yet been completed. In this study, we determined the lowest lying structures of ThC13+ and UC13+ clusters using an unbiased structural search method. The 13-coordinate planar ring configuration was the most stable for both ThC13+ and UC13+ cluster cations. The C-An bonds in ThC13+ and UC13+ show a small degree of covalency, originating from the overlap of the s, d, and f orbitals of the An atoms with C 2p orbitals of both π and σ characteristics. The infrared and electronic absorption spectra of the most favorable planar ring configurations were theoretically simulated to facilitate the identification of the molecular structures in future experiments. This study provides an in-depth understanding of the experimental mass spectra.

Unveiling siliborophene's potential as an anode material for advancing Li ion batteries: DFT and ab-initio molecular dynamics

A favorable anodic candidate with significant potential is currently in high demand for Lithium-ion batteries. The χ3 borophene, a two-dimensional material, shows potential as an anode in Li-ion batteries. However, its original structure requires improvement to enhance its Li diffusivity and specific capacity. This research investigates the modification of χ3 borophene by silicon atoms, resulting in a new structure called siliborophene, using density functional theory. Ab-initio molecular dynamics simulations confirm the stability of siliborophene structure at room temperature. The Siχ3 structure hosts adsorption sites for the Li atom, and after exploring various positions, the most favorable configuration exhibits an adsorption energy of −1.33 eV. The siliborophene surface can adsorbed up to 13 Li atoms but according to the further analyses the results of open-circuit voltage suggest that the siliborophene structure can store 10 Li atoms, so Li10Siχ3 structure is considered as the structure with maximum adsorption capacity. The interaction between the surface and Li atoms is stronger in this configuration, with −1.10 eV adsorption energy which yields a maximum specific capacity of 1291 mAh/g. Analysis of the partial density of states and band structure reveals metallic characteristics of the surface during lithiation. Furthermore, using the CI-NEB approach, the barrier activation energy for Li diffusion was calculated, showing exceptionally low values at 0.32 eV, enabling rapid Li diffusion on the surface. These findings indicate that siliborophene holds promise as a potential anode material for lithium-ion batteries.

A Workflow for Identifying Viable Crystal Structures with Partially Occupied Sites Applied to the Solid Electrolyte Cubic Li7La3Zr2O12.

To date, experimental and theoretical works have been unable to uncover the ground-state configuration of the solid electrolyte cubic Li7La3Zr2O12 (c-LLZO). Computational studies rely on an initial low-energy structure as a reference point. Here, we present a methodology for identifying energetically favorable configurations of c-LLZO for a crystallographically predicted structure. We begin by eliminating structures that involve overlapping Li atoms based on nearest neighbor counts. We further reduce the configuration space by eliminating symmetry images from all remaining structures. Then, we perform a machine learning-based energetic ordering of all remaining structures. By considering the geometrical constraints that emerge from this methodology, we determine that a large portion of previously reported structures may not be feasible or stable. The method developed here could be extended to other ion conductors. We provide a database containing all of the generated structures with the aim of improving accuracy and reproducibility in future c-LLZO research.

Tuning the thermoelectric properties of graphene nanoribbons by vacancy defect with Ge-doping

In this work, the influence of vacancy defects and germanium (Ge)-doping on structural stability, electronic and thermoelectric (TE) characteristics of armchair graphene nanoribbons (AGNRs) have been studied by density functional theory (DFT) based tight-binding coupled with nonequilibrium green function (NEGF) calculations. Three concentrations of Ge impurities, single, two, and three, are identified at different sites with vacancy defects. As a result, the DFT calculations suggest that the defected AGNRs with three Ge impurities are structurally favorable configurations due to the lowest required cohesive energy. At low doping ratio, small bandgap for defected AGNRs is predicted leading to high Seebeck coefficient and figure of merit. In contrast, at high doping ratio, low Seebeck coefficient and figure of merit are noticed. The results show that the TE properties of AGNRs do not only depend on the Ge concentrations with vacancy defect but also depend on the geometrical pattern of Ge impurities. As a result, exploiting the electronic and thermoelectric properties of AGNRs to create nanostructure, which can be used in many important applications for nanoelectronics and spintronics.

Theoretical Evaluation of the Properties of Nitrogen-Doped C24 Fullerenes and Their Interactions with Two Adamantane-Derived Antivirals

The replacement of carbon with a heteroatom within the structure of a fullerene gives the possibility of obtaining compounds with adjustable properties. The influence of aza-substitution on C24 fullerenes was investigated and a comparison of HF and DFT calculations was performed. Various substitution patterns were proposed and the characterization of C22N2 and C20N4 structures was performed. Global reactivity descriptors like chemical potential, hardness, HOMO–LUMO gap and singlet–triplet gap were computed. Aromaticity descriptors like delocalization indices and NICS(0) index were employed for the characterization of each six-membered ring of the studied fullerenes. The possible use of aza-fullerenes as drug delivery systems for two adamantane-derived antivirals was evaluated through molecular docking studies. The best results were obtained for the fullerenes with a pronounced hydrophobic character, the favored configuration of the antiviral drugs being the one oriented toward the side consisting of carbon atoms of the fullerenes.

Enhanced energization of plume ions around Mars from interplanetary shocks

Heavy ions escaping Mars along the solar wind electric field direction are often referred to as an “ion plume”. This phenomenon represents one of the major ion escape channels on Mars. Spacecraft observations have indicated that the global average of escaping ion fluxes, derived with the aid of models, can be increased by an order of magnitude or more in response to strong solar events. In particular, it has been reported that interplanetary (IP) shocks produce high-energy escaping ion plumes. However, the ion acceleration mechanisms associated with the shock arrival have not yet been fully elucidated. During the passage of an IP shock on Mars on March 3, 2015, the plume O+ ions continuously entered the narrow field of view (FoV) of STATIC on board the MAVEN spacecraft, thanks to favorable FoV configurations. This event provides a unique opportunity to identify plume ion energization processes associated with the shock arrival. Our analysis suggests that the enhanced energization of the plume O+ ions is mainly due to the enhanced convection electric field caused by the IP shock compression. This finding provides a crucial clue towards the understanding of how IP shocks facilitate ion escape through the plume.

Graphdiyne/main-group metal elements sandwich structure as a promising single atom electrocatalyst for nitrogen reduction: A theoretical investigation

In an effort to limit global warming and CO2 emission, ammonia has become a viable hydrogen carrier and alternative fuel. Electrocatalytic nitrogen reduction (e-NRR) has gained much attention as a mean to produce ammonia under mild reaction conditions. Consequently, the advancement of highly efficient and selective catalysts for e-NRR is key in the development of clean energy. Based on the "chainmail" protection catalyst proposed by recent studies, we used first-principles calculations to design a catalyst composed of a single main-group metal atom sandwiched between BN-doped graphdiyne and graphdiyne sheets. The structures, labeled BN-M-G (M = Li, Na, K, Mg, Ca and Al), were investigated as potential catalysts for e-NRR. After screening the most favorable configurations for N2 adsorption and activation, we further explored their e-NRR catalytic properties including efficiency and selectivity. Our results show that the optimal e-NRR path on BN-Mg-G and BN-Al-G is the alternating path with a limiting voltage of -0.47 V and -0.67 V, respectively. In contrast to the competing reaction, hydrogen evolution reaction (HER), both catalysts show high selectivity towards e-NRR. Our work shows that through rational design and electronic structure regulation, main-group-metals-based catalysts can have comparable catalytic activity as transition metal catalysts. This present study offers new insights for the development of low-cost and environmetally-friendly main group metal catalysts.