Structure Of Clusters Research Articles

Optimizing the structure of acene clusters.

We present a study of the potential energy surface of anthracene, tetracene, and pentacene clusters with up to 30 molecules. We have applied the basin-hopping Monte Carlo algorithm to clusters of acene molecules in order to find their lowest energy states. The acene molecules are described by the polymer-consistent force field-interface force field. We present the structures with the lowest observed energy, and we discuss the relative stability and accessibility of structures corresponding to local energy minima.

Tailoring the Asymmetric Structure of NH2‐UiO‐66 Metal‐Organic Frameworks for Light‐promoted Selective and Efficient Gold Extraction and Separation

AbstractDesigning adsorption materials with high adsorption capacities and selectivities is highly desirable for precious metal recovery. Desorption performance is also particularly crucial for subsequent precious metal recovery and adsorbent regeneration. Herein, a metal–organic framework (MOF) material (NH2‐UiO‐66) with an asymmetric electronic structure of the central zirconium oxygen cluster has an exceptional gold extraction capacity of 2.04 g g−1under light irradiation. The selectivity of NH2‐UiO‐66 for gold ions is up to 98.8 % in the presence of interfering ions. Interestingly, the gold ions adsorbed on the surface of NH2‐UiO‐66 spontaneously reduce in situ, undergo nucleation and growth and finally achieve the phase separation of high‐purity gold particles from NH2‐UiO‐66. The desorption and separation efficiency of gold particles from the adsorbent surface reaches 89 %. Theoretical calculations indicate that ‐NH2functions as a dual donor of electrons and protons, and the asymmetric structure of NH2‐UiO‐66 leads to energetically advantageous multinuclear gold capture and desorption. This adsorption material can greatly facilitate the recovery of gold from wastewater and can easily realize the recycling of the adsorbent.

A point selection method in map generalization using graph convolutional network model

ABSTRACT For point clusters, the conflict and crowding of map symbols is an inevitable problem during the transition from large to small scales. The cartographic generalization involved in this problem as a spatial decision-making process is usually related to the analysis of spatial context, the choice of abstraction operators, and the judgment of the resulting data quality. The rules summarized by traditional generalization methods usually require manual setting of conditions or thresholds and sometimes encounter special cases that make it difficult to directly match certain rules or integrate different rules together. An alternative method is using a data-driven strategy under AI technology background to simulate cartographer behaviors through typical sample training, such as deep learning. The integration of cartography domain knowledge and deep learning is a better choice to settle generalization decisions. This study uses a combination of domain knowledge and a data-driven approach to introduce graph neural networks into point cluster generalization. First, we construct a virtual graph structure of point clusters using Delaunay triangulation, secondly, we extract spatial features, contextual features, and attributes of each point separately, and then propose a generalization model based on the TAGCN network. Finally, this model is trained with the manually generalized sample to realize the automatic point cluster generalization. The results demonstrate that the proposed model is valid and efficient for point cluster generalization and that this algorithm can better maintain various characteristics of the point cluster in both the local area and the overall map compared to other methods.

Tailoring the Asymmetric Structure of NH2 -UiO-66 Metal-Organic Frameworks for Light-promoted Selective and Efficient Gold Extraction and Separation.

Designing adsorption materials with high adsorption capacities and selectivities is highly desirable for precious metal recovery. Desorption performance is also particularly crucial for subsequent precious metal recovery and adsorbent regeneration. Herein, a metal-organic framework (MOF) material (NH2 -UiO-66) with an asymmetric electronic structure of the central zirconium oxygen cluster has an exceptional gold extraction capacity of 2.04 g g-1 under light irradiation. The selectivity of NH2 -UiO-66 for gold ions is up to 98.8 % in the presence of interfering ions. Interestingly, the gold ions adsorbed on the surface of NH2 -UiO-66 spontaneously reduce in situ, undergo nucleation and growth and finally achieve the phase separation of high-purity gold particles from NH2 -UiO-66. The desorption and separation efficiency of gold particles from the adsorbent surface reaches 89 %. Theoretical calculations indicate that -NH2 functions as a dual donor of electrons and protons, and the asymmetric structure of NH2 -UiO-66 leads to energetically advantageous multinuclear gold capture and desorption. This adsorption material can greatly facilitate the recovery of gold from wastewater and can easily realize the recycling of the adsorbent.

Evolution of binary stars in the early evolutionary phases of ultra-faint dwarf galaxies

ABSTRACT The dynamics of binary stars provides a unique avenue to gather insight into the study of the structure and dynamics of star clusters and galaxies. In this paper, we present the results of a set of N-body simulations aimed at exploring the evolution of binary stars during the early evolutionary phases of ultra-faint dwarf galaxies (UFD). In our simulations, we assume that the stellar component of the UFD is initially dynamically cold and evolves towards its final equilibrium after undergoing the violent relaxation phase. We show that the early evolutionary phases of the UFD significantly enhance the disruption of wide binaries and leave their dynamical fingerprints on the semimajor axis distribution of the surviving binaries as compared to models initially in equilibrium. An initially thermal eccentricity distribution is preserved except for the widest binaries for which it evolves towards a superthermal distribution; for a binary population with an initially uniform eccentricity distribution, memory of this initial distribution is rapidly lost for most binaries as wider binaries evolve to approach a thermal/superthermal distribution. The evolution of binaries is driven both by tidal effects due to the potential of the UFD dark matter halo and collisional effects associated to binary–binary/single star encounters. Collisional effects are particularly important within the clumpy substructure characterizing the system during its early evolution; in addition to enhancing binary ionization and evolution of the binary orbital parameters, encounters may lead to exchanges of either of the primordial binary components with one of the interacting stars.

How ligand coordination and superatomic-states accommodate the structure and property of a metal cluster: Cu4(dppy)4Cl2vs. Cu21(dppy)10 with altered photoluminescence

We have synthesized two copper nanoclusters (NCs) with a protection of the same ligand diphenylphosphino-2-pyridine (C17H14NP, dppy for short), formulated as Cu4(dppy)4Cl2 and Cu21(dppy)10, respectively. The former one bears a distorted tetrahedron Cu4 core with its six edges fully protected by chlorine and dppy ligands, while the latter presents a symmetric Cu21 core on which ten dppy molecules function as monolayer protection via well-organized monodentate or bidentate coordination. Interestingly, the Cu4(dppy)4Cl2 cluster exhibits a strong yellow emission at ∼577 nm, while Cu21(dppy)10 displays dual emissions in purple (∼368 nm) and green (∼516 nm) regions respectively. In combination with TD-DFT calculations, we demonstrate the origin of altered emissions and unique stability of the two copper nanoclusters pertaining to the ligand coordination and metallic superatomic states.

17O hyperfine spectroscopy in surface chemistry and catalysis

Oxide-based materials are of key technological importance in different areas including advanced functional materials, solid state chemistry and catalysis. Many of the key questions concerning these areas involve understanding the chemical bond between the metal and the oxygen ions in the first or subsequent coordinating shells. The spectroscopic study of oxygen is therefore of fundamental importance to elucidate the complex interfacial coordination chemistry that underlies the development of metal-oxide supported catalysts and other advanced materials. Oxygen atoms at solid surfaces or lining the pores of zeolite frameworks play a vital role in stabilizing and defining the electronic and geometric structure of single metal atoms or clusters that act as catalytically active sites. In the case of paramagnetic species, EPR and its related hyperfine techniques offer a unique opportunity to explore and understand the nature of the chemical bonding in metal-oxide systems through the detection of the 17O hyperfine interaction. In this perspective we offer an overview of experimental considerations and relevant examples specific to 17O hyperfine spectroscopy of transition metal ions in zeolites relevant to catalysis. 17O hyperfine coupling values are obtained, which allow discriminating σ- and π-bonding channels in metal-oxygen bonds involving first-row transition metal ions. An exhaustive collection of 17O hyperfine and nuclear quadrupole couplings in different systems including molecular and biomolecular chemistry is provided, emphasizing the connection between interfacial and molecular inorganic coordination chemistry.

Structure and stability of Au, Au2 and Au8 cluster on Ni(111) supported h-BN sheet: Role of size and support towards oxygen bond activation

Atomic level heterogenous catalysis has been of importance for in-depth understanding and designing of novel catalytic material. Present work aims to investigate the chemical reactivity of Au, Au 2 and Au 8 cluster on hexagonal boron nitride nano sheet (h-BN) and its Ni(111) activated analogue using density functional theory (DFT). The average vertical separation of gold atom(s) from h-BN is significantly influenced by Ni(111) support. Oxygen molecule, which is the key reactant for any oxidation reaction, is considered as probe molecule to verify the reactivity. Contrary to the case of Au atom, which is the most reactive on free-standing h-BN, Au 2 and Au 8 clusters show higher reactivity on Ni supported h-BN. Thus the agglomeration of Au (Au–Au interaction) and Ni(111) support is important in controlling the reactivity and therefore, will play a key role to design Au based efficient catalyst for future. • On free-standing h-BNNS, Au atom and Au dimer favours on top B and N atoms, respectively. • With Ni (111) supported h-BNNS both Au and Au 2 favour on-top B atom. • On free-standing h-BNNS, Au elongates the O–O bond more than Au 2 and Au 8 . • On Ni (111) supported h-BNNS, the O–O bond elongation is maximum on Au 8 cluster. • The presence of Ni(111) support improves the catalytic activity by spin modulation of the B atoms of h-BNNS.

An Atomistic View of Platinum Cluster Growth on Pristine and Defective Graphene Supports (Small 10/2023)

Pristine and Defective Graphene Supports As platinum-based materials are among the most efficient catalysts for the electrochemical processes in proton exchange membrane fuel cells, especially for the oxygen reduction reaction, several groups have shown that the support material has a major influence on the coordinative stabilization and especially on the modification of the reactivity of the Pt-cluster-graphene combined material. In article number 2207484, Christoph Jung, Timo Jacob, and co-workers investigate the growth and electronic structure of platinum clusters adsorbed on pristine and defective graphene supports using density functional theory calculations.

Identification of the precursor cluster in thermolysin crystallization solution by molecular dynamics methods

An analysis of the crystal structure of thermolysin revealed four possible precursor clusters (hexamers) of its crystal. Using the method of molecular dynamics and plots of root mean square fluctuation, root mean square deviation and radius of gyration, the most stable hexamer, which is a precursor cluster,was determined. The importance of the established structure of the thermolysin precursor cluster for determining the mechanism of crystal formation is shown.

ISSUES OF DEVELOPING THE CONTENT OF MAP OF AGRO-INDUSTRIAL CLUSTERS OF SURKHANDARYA REGION

The article is devoted to the development of maps of agro-industrial clusters operating in the Surkhandarya region. The agro-industrial complex, its structure and significance, the cluster approach, as well as the territorial and sectoral structure of the agro-industrial clusters of the region are considered. The article developed content elements for several maps of agro-industrial clusters of the Surkhandarya region. Certain methods of cartographic representation and visual means are recommended for displaying each element of the thematic content. At the same time, examples of directions for using maps of agro-industrial clusters of the Surkhandarya region are given.

CLUSTER AS THE BASIS FOR THE SUSTAINABLE FUNCTIONING OF ENTERPRISES IN THE AGRO-INDUSTRIAL COMPLEX

Objective. This article is devoted to the analysis of the concept of an agro-industrial cluster and the development of recommendations for improving competitiveness in the agro-industrial complex.
 Materials and methods. The research methodology is based on the collection and analysis of initial data and information. The article uses a systematic approach to the study of socio-economic processes and phenomena. The study is based on modern theories of competition, innovation, as well as the modern paradigm of the cluster development of the economy.
 Results. The conducted research makes a certain contribution to the development of theoretical science. A model of the structure of a regional industrial agricultural cluster is proposed. Practical recommendations can be used by economic and state authorities, heads of agricultural organizations, peasant (farm) enterprises, LPH.
 Conclusion. It is concluded that the characteristic features of the cluster and the effects arising in it increase the competitiveness of both individual members of the cluster and the cluster as a whole, and the competitiveness of the region in which the cluster is located, which, in turn, leads to an increase in the competitiveness of the national economy.

Модель формування пористості брикетів губчастого титану на стадії спікання

This article examines the peculiarities of the formation of interparticle connections in porous products based on titanium powders using sponge titanium as an example, which are used in the aviation industry and airfield management. The developed model is based on the results of a previous study, where the structure of cuboctahedral and inverse cuboctahedral clusters of packing spherical powder particles was determined at the most dense packing. During the study, a model of the fusion of particles at the points of pressing deformation due to recrystallization under the influence of high temperatures in a vacuum was developed. 4 main stages of powder briquette sintering were considered, and a mathematical model was developed for each of them. Thus, the stage of liquid evaporation is considered from the viewpoint of the cavitation effect of boiling on the surface of particles and boiling of plasticizers. Euler's film boiling formula was used to describe the forces acting on the particle surface; Tolubinsky's formula was used for bubble boiling; convective heat exchange was considered part of the final stage of sintering. The stage of the formation of metallic bonds is modeled on the basis of the results of practical studies in the REV 5.5 furnace, recrystallization based on differential scanning colorimetry on the NETZSCH STA 449F1 Proteus device, and determining the change in grain size according to the E19 ASTM scales using the Jeffers method. The diffusion stage is modeled on the basis of the approximation of the particle deformation model in the contact zones at the pressing stage using the Frenkel formula. Linear shrinkage is modeled based on direct measurement of sample sizes before and after sintering. The developed model has a certain versatility when applied to simulate the interaction of particles of metal powders under the conditions of the formation of porous briquettes, especially if the shape of the particles is close to round or spongy. The obtained result will make it possible to more accurately evaluate such a factor as the adhesion between the particles of the pressing and predict the tensile strength of the material. Additionally, due to the mathematical characterization of the peculiarities of the formation of corpuscular porosity under the conditions of sintering in a vacuum, we can design materials with differentiated porosity, as well as lay the foundations for powder 3D printing of such materials, by assembling grain by grain, or layer by layer with the adjustment of the force of particle compression one into the other.

Coordination-number-determined activity of copper catalyst in water-gas shift reaction

The water–gas shift reaction (WGSR) is of great significance in industrial hydrogen production. In this paper, Cun/TiO2(n = 1,2,4,8) and Cu (111) crystal planes were studied to explore the effect of size effect on the activity of WGSR. Density functional theory (DFT) calculations showed that the adsorption energy of H2O molecule was significantly enhanced on the surface of Cu1 and Cu2 clusters compared with Cu4 and Cu8 clusters, while CO adsorption strength first increased and then decreased. Among many copper clusters of different sizes, the redox pathway cannot proceed due to the lack of active sites on Cu1 and Cu2 clusters. According to the analysis of the microkinetic model, the order of WGSR activity on the surface of copper clusters of different sizes is: Cu4 > Cu2 ≈ Cu8 > Cu1 > Cu (111). The active center structure of the copper cluster is composed of 3 copper atoms in which the Cu-Cu coordination number is ca. 2 ∼ 3, and the active center is partially oxidized copper. Essentially, the low-coordination copper atoms determined by the geometry structure promote the WGSR activity of the copper clusters. This work not only reveals the copper cluster size effect on WGSR, but also provides the guidance for the size design and control of other supported metal catalysts.

A study of the valence photoelectron spectrum of uracil and mixed water-uracil clusters.

The valence ionization of uracil and mixed water-uracil clusters has been studied experimentally and by ab initio calculations. In both measurements, the spectrum onset shows a red shift with respect to the uracil molecule, with the mixed cluster characterized by peculiar features unexplained by the sum of independent contributions of the water or uracil aggregation. To interpret and assign all the contributions, we performed a series of multi-level calculations, starting from an exploration of several cluster structures using automated conformer-search algorithms based on a tight-binding approach. Ionization energies have been assessed on smaller clusters via a comparison between accurate wavefunction-based approaches and cost-effective DFT-based simulations, the latter of which were applied to clusters up to 12 uracil and 36 water molecules. The results confirm that (i) the bottom-up approach based on a multilevel method [Mattioli et al. Phys. Chem. Chem. Phys. 23, 1859 (2021)] to the structure of neutral clusters of unknown experimental composition converges to precise structure-property relationships and (ii) the coexistence of pure and mixed clusters in the water-uracil samples. A natural bond orbital (NBO) analysis performed on a subset of clusters highlighted the special role of H-bonds in the formation of the aggregates. The NBO analysis yields second-order perturbative energy between the H-bond donor and acceptor orbitals correlated with the calculated ionization energies. This sheds light on the role of the oxygen lone-pairs of the uracil CO group in the formation of strong H-bonds, with a stronger directionality in mixed clusters, giving a quantitative explanation for the formation of core-shell structures.

Algebraic Graph-Based Machine Learning Model for Li-Cluster Prediction.

In cluster research, determining the ground-state structure of medium-sized clusters is hindered by a large number of local minimum on potential energy surfaces. The global optimization heuristic algorithm is time-consuming due to the use of DFT to determine the relative size of the cluster energy. Although machine learning (ML) is proved to be a promising way to reduce the DFT computational costs, a suitable method to represent clusters as input vectors is one of the bottlenecks in the application of ML to cluster research. In this work, we proposed a multiscale weighted spectral subgraph (MWSS) as an effective low-dimension representation of clusters and build an MWSS-based ML model to discover the structure-energy relationships in lithium clusters. We combine this model with the particle swarm optimization algorithm and DFT calculations to search for globally stable structures of clusters. We have successfully predicted the ground-state structure of Li20.

Rotational dive into the water clusters on a simple sugar substrate

Most biomolecular activity takes place in aqueous environments, and it is strongly influenced by the surrounding water molecules. The hydrogen bond networks that these water molecules form are likewise influenced by their interactions with the solutes, and thus, it is crucial to understand this reciprocal process. Glycoaldehyde (Gly), often considered the smallest sugar, represents a good template to explore the steps of solvation and determine how the organic molecule shapes the structure and hydrogen bond network of the solvating water cluster. Here, we report a broadband rotational spectroscopy study on the stepwise hydration of Gly with up to six water molecules. We reveal the preferred hydrogen bond networks formed when water molecules start to form three-dimensional (3D) topologies around an organic molecule. We observe that water self-aggregation prevails even in these early stages of microsolvation. These hydrogen bond networks manifest themselves through the insertion of the small sugar monomer in the pure water cluster in a way in which the oxygen atom framework and hydrogen bond network resemble those of the smallest three-dimensional pure water clusters. Of particular interest is the identification, in both the pentahydrate and hexahydrate, of the previously observed prismatic pure water heptamer motif. Our results show that some specific hydrogen bond networks are preferred and survive the solvation of a small organic molecule, mimicking those of pure water clusters. A many-body decomposition analysis of the interaction energy is also performed to rationalize the strength of a particular hydrogen bond, and it successfully confirms the experimental findings.

Investigating the structural and electronic properties of anionic calcium-doped magnesium clusters

In recent years, the structure and properties of alkaline earth metal-doped Mg clusters have attracted much attention. Here, we investigated the structural properties, stability analysis, chemical bonding properties and charge transfer properties of Ca2Mgnˉ (n=1-15) nanoclusters by using the efficient CALYPSO structure search software and the DFT full domain search method based on B3PW91 level calculation. It is found that most of their ground state structures can inherit pure Mgn+2ˉ (n=1-15) clusters with high symmetry. We further compare the experimental and theoretical PES spectral data using pure Mgn+2ˉ (n=1-15) and find a high agreement, which also indicating the validity of my calculated all-domain most stable structure. We found the outstanding stability of the pentagonal Ca2Mg7ˉ by stability analysis. Charge transfer occurred in all Ca2Mgnˉ clusters, and this transfer was from Ca to Mg. The chemical bonding properties and molecular orbital revealed that the contribution of Mg-s and Mg-p to the molecular orbitals led to the formation of strong Mg-Mg bonds in the Ca2Mg7ˉ cluster, the s-p hybridization between Ca and Mg atoms and between Mg and Mg atoms also led to more powerful Mg-Mg bonds and Ca-Mg bonds, which is strong evidence for the stability of the Ca2Mg7ˉ clusters.

Zr Oxo Cluster for Cascade Conversion of Furfural to Alkyl Levulinates

AbstractA novel dodecanuclear Zr oxo cluster [Zr6O4(OH)4 (HSCH2CH2COO)12]2 (ZrO‐SH‐10) has been constructed under the room temperature, followed by oxidation of the sulfhydryl group with H2O2 to achieve a bifunctional catalyst with Lewis acid and Brönsted acid sites. The characterization of catalysts indicated that {Zr6O4} cluster core can be stabilized with a shell of carboxylate ligands, and the resulting ZrO‐SO3H was formed as a discrete molecular catalyst, exhibiting superior activity and recyclability for the cascade conversion of furfural to alkyl levulinate by the integration of transfer hydrogenation and alcoholysis in n‐butanol. The yield of n‐butyl levulinate can achieve as high as 91 % under the optimum conditions. Meanwhile, no leaching of the active species was found, which confirmed the structure of the Zr oxo cluster was air and moisture‐stable. On the basis of the studies on the reaction kinetics and isotope tracking, the reaction mechanism was proposed accordingly.

Super-resolved SIM imaging revealed hierarchical organization of the ryanodine receptor network in 3 dimensions in rabbit sinoatrial node cells.

The heartbeat is initiated by specialized sinoatrial node cells (SANCs). The rate of the heartbeat is regulated by Ca released from the sarcoplasmic reticulum (SR) via ryanodine receptors (RyRs) interacting with voltage and Ca-dependent membrane ion currents in SANCs. The released Ca takes the form of localized Ca releases (LCRs) that propagate for limited distances in wave-like manner. A computational model of SANCs, previously developed in our laboratory, simulates LCR synchronization mechanism as hierarchical clustering of surface RyRs based on confocal microscopy imaging data obtained in tangential sections of SANCs. The true detailed distribution of RyR clusters in 3D, however, remains unknown. Here, we applied a series of new computational approaches to experimental data obtained by super-resolved structured illumination microscopy in rabbit SANCs, in which RyRs were labeled by specific antibodies. Our approach consists of automated segmentation of RyR clusters with globally optimal detection and segmentation of objects with constant internal intensity distribution, followed by object-based colocalization analysis in 3D. Results are further refined with watershed transformations and computational geometry. Examinations of the images have revealed a hierarchical architecture of RyR network (positions and sizes of submembrane RyR clusters). After constructing a mathematical convex hull around the cell using RyR clusters as nodes, clusters were grouped based on their volume. The distribution of RyR clusters exhibited a wide range of sizes from 0.75 × 10−3 µm3 to 0.50 µm3 and cluster histograms followed a Poisson-like distribution. These new data have been incorporated in a new, realistic 3D model of SANC, in which heterogeneous RyR clusters facilitate LCR propagation. Impairment of the complex, hierarchical structure of RyR clusters may lead to sinus node dysfunction in aging and disease.