Atoms In Cluster Research Articles

Structural, electronic, thermodynamic and optical properties of SnlSemSn clusters: A DFT study

• DFT study of electronic, thermodynamic and optical properties of SnlSemSn clusters. • Band gap energy of Sn l Se m S n clusters lie in the semiconducting range (1.035–3.463 eV). • Sn 1 Se 1 S 2 is found to be the most reactive cluster. • Absorption spectra can be tailored by varying thecomposition of atoms in clusters. Density Functional Theory (DFT) calculations are performed to investigate the structural, electronic, thermodynamic, and optical properties of Sn l Se m S n clusters with the variation in the number of Sn, Se, and S atoms using B3LYP/321-G ∗ level of theory. We have obtained 23 optimized clusters and their calculated properties are dependent on the size, geometry, and structure of clusters. We observed that Sn 1 Se 1 S 2 is found to be highly reactive owing to its largest values of electronegativity, vertical ionization potential, vertical electron affinity with the least values of binding energy and band gap energy. The least reactive cluster is Sn 1 Se 1 S 8 with the maximum values of band gap and hardness. The band gap energies of all clusters lie in the semiconducting range (1.035 eV–3.463 eV). The optical absorption is observed in ultraviolet and visible regions. The theoretically computed absorption spectrum for excited states is compared experimentally confirming their applications in optoelectronics.

Stability and electronic properties of V-doped ruthenium nanoclusters and their adsorptive properties towards hydrogen sulphide and serine molecules

The stability and electronic properties of the RunV (n = 2–10) nanoclusters and their interaction with hydrogen sulphide and serine molecules were conducted using DFT calculations at the PBE/LanL2DZ/6-311G(d,p) level of theory. The results indicate that the Ru3V, Ru5V and Ru7V clusters were found to be more stable than their neighbouring clusters, and the V atom in the binary clusters has been viewed as the most favourable adsorption site for a nucleophilic attack. The interaction of H2S with the clusters easily leads to its dissociation into *SH and *H moieties, indicating that the dissociative adsorption was found to be more favourable than the molecular adsorption. This finding suggest that these clusters could be employed as nanocatalysts for the H2S decomposition reaction. In contrast, the serine adsorption over the surface of the RunV clusters was carried out without dissociation with adsorption energies which vary from - 29.3 to - 58.7 kcal mol−1, suggesting a chemisorption process. The adsorption of the serine molecule on the RunV (n = 3, 7 and 10) clusters causes a significant change in their energy gaps, indicating a high electronic sensitivity of these clusters towards the serine molecule.

Conversion of stacking fault tetrahedra to bubbles in dual (Kr, He)-beam irradiated copper

Stacking fault tetrahedrons (SFTs) are commonly observed in irradiated face-centered-cubic metals with low-to-medium stacking fault energies. Several mechanisms were previously proposed for the removal of SFTs in irradiated solids, including high temperature annealing, interactions with interstitial atoms, dislocations, and twin boundaries, and transformation to dislocation loop under compressive stress. We propose a previously unreported mechanism for the removal of SFT in irradiated copper, supported by experiments and atomistic simulations. In situ experiments showed that helium bubble density increased at the expense of SFT density following the initial phase of dual 1 MeV Kr/12 keV He ion irradiation, suggesting a possible conversion of SFTs to helium bubbles. Atomistic simulations of the interactions of helium atoms with SFTs confirmed this possibility and revealed the collective effects of helium-induced shear stress that deformed the atomic planes of Cu leading to the destruction of the SFT and leaving behind helium atoms in vacancy clusters (bubbles).

The structure of anionic NbH n − (n = 2–15) clusters and their maximum hydrogen capacity

The geometrical structures of the lowest energy states of anionic niobium-doped hydrogen clusters are determined based on Crystal structure AnaLYsis by the Particle Swarm Optimization (CALYPSO) isomer search method. The geometries and relative stabilities are determined by the B3LYP hybrid density functional theory (DFT) method. The calculated results show that a niobium atom can absorb up to twelve hydrogen atoms in the anionic clusters. In exploring the stability, electronic properties, and photoelectron spectra of NbH n − clusters, the NbH12 − cluster is found to possesses a relatively high binding energy, high second-order differential energy, and a large HOMO–LUMO gap. The hydrogen storage density of the NbH12 − cluster is calculated as 11.5 wt%. The present findings enrich the database of transition metal doped hydrogen clusters and the insights are important in the pursuit of efficient hydrogen energy storage materials.

The preliminary exploration of composition origin of solid solution alloys used in thermocouple by cluster-plus-glue-atom model

The chemical composition proportion of solid solution alloys in thermocouples (TCs) field is preliminarily explored by the cluster-plus-glue-atom (CPGA) model. CPGA clusters for face-centered cubic (fcc) and body-centered cubic (bcc) structure elemental metal are established, which are the cubic octahedron and rhombic dodecahedron respectively. With introducing the solute A element into solvent B matrix, the solute A atoms will prefer to the certain sites of solvent B atoms in CPGA cluster. Setting a CPGA cluster consisted of solute A and solvent B atoms as the central cluster, Friedel oscillation perturbation of central cluster on surrounding CPGA clusters will be totally shielded along radial at the position of 3 times of size of central cluster. Then, CPGA unit clusters for fcc and bcc structure solid solution alloys are established, which consist of the central, nearest neighbor, and glue clusters. Take K type TCs as an example. The nominal and theoretical stable composition proportion for Ni-Cr/Ni-Si solid solution alloys are Ni90Cr10/Ni97Si3 (wt. %) and Ni96.9Si3.1/Ni89.5Cr10.5 (wt. %), which correspond well with each other. Finally, CPGA unit clusters for most solid solution alloys in TCs field are analyzed, which display the better correspondence to the nominal composition proportion of them.

Post-modification of metal-organic framework for improved CO2 photoreduction efficiency

Utilizing metal-organic frameworks (MOFs) to design photocatalysts for CO2 reduction catalysts is an excellent idea but currently restricted by the relatively low activity. Enhancing CO2 affinity and tuning the oxidation state of metal clusters in MOFs might be a solution to improve the catalytic performance. Herein, the Cl-bridge atoms in the metal clusters of a cobalt MOF were easily exchanged with OH−, which simultaneously oxidized a portion of Co(II) to Co(III) and resulted in a much enhanced photocatalytic activity for CO2 reduction. In contrast, the original framework does not exhibit such superior activity. Comprehensive characterizations on their physicochemical properties revealed that the introduction of hydroxyl group not only greatly increases the CO2 affinity but also alters the oxidation state of metal clusters, resulting in significantly improved photocatalytic activities for CO2 reduction. This work provides important insight into the design of efficient photocatalysts.

Tuning precise numbers of supported nickel clusters on graphdiyne for efficient CO2 electroreduction toward various multi-carbon products

Compared to single-atom catalysts, supported metal clusters can exhibit enhanced activity and designated selectivity in heterogeneous catalysis due to their unique geometric and electronic features. Herein, by means of comprehensive density functional theory (DFT) computations, we systematically investigated the potential of several Ni clusters supported on graphdiyne (Nix/GDY, x = 1–6) for CO2 reduction reaction (CO2RR). Our results revealed that, due to the strong interaction between Ni atoms and sp-hybridized C atoms, these supported Ni clusters on GDY exhibit high stabilities and excellent electronic properties. In particular, according to the computed free energy profiles for CO2RR on these Nix/GDY systems, the anchored Ni4 cluster was revealed to exhibit high CO2RR catalytic activity with a small limiting potential and moderate kinetic barrier for C–C coupling, and CH4, C2H5OH, and C3H7OH were identified as the main products, which can be attributed to its strong capacity for CO2 activation due to its unique configuration and excellent electronic properties. Thus, by carefully controlling the precise numbers of atoms in sub-nano clusters, the spatially confined Ni clusters can perform as promising CO2RR catalysts with high-efficiency and high-selectivity, which may provide a useful guidance to further develop novel and low-cost metal clusters-based catalysts for sustain CO2 conversion to valuable chemicals and fuels.

Interpreting the Operando X-ray Absorption Near-Edge Structure of Supported Cu and CuPd Clusters in Conditions of Oxidative Dehydrogenation of Propane: Dynamic Changes in Composition and Size

Supported subnano-cluster catalysts are highly dynamic, developing true active sites only under the pressures and temperatures of reaction conditions. Operando X-ray absorption near-edge structure (XANES) spectroscopy can track changes in the oxidation state and the local environment of cluster atoms, providing insight into the development of these active sites. While bulk metal, oxide, and hydroxide standards are often used for fitting experimental XANES spectra to obtain average oxidation states, we recently showed that computed cluster standards of relevant compositions are a more suitable basis, producing more accurate fits. Here, we theoretically interpret the operando XANES of supported Cu3Pd and Cu4 clusters during temperature-programmed reaction (TPRx) of oxidative dehydrogenation of propane. We use an expanded basis set including both globally optimized computed clusters and bulk standards. Not only can we track reversible composition/oxidation state change with temperature, but also the irreversible growth of the bulk fraction upon heating, which we attribute to cluster sintering. This has important implications for the mechanism of the catalyzed reaction and the nature of the available active sites. We propose that operando XANES provides most significant insight into the nature of supported cluster catalysts in reaction conditions when interpreted using mixed computed cluster and bulk standards.

C – C coupling of ethyne to the carbido ligand in products from reactions with Ru5(μ5[sbnd]C)(CO)15

The reaction of Ru5(μ5-C)(CO)15, 1 with C2H2 at 48 °C for 60 h yielded four new pentaruthenium carbonyl cluster compounds: Ru5[μ5-η5-CC(H)C(H)C(H)C(H)](CO)13(μ4-η2-HCCH), 2; Ru5[μ4-η5-CC(H)C(H)C(H)C(H)](CO)12(μ4-η2-HCCH), 3; Ru5(CO)13[μ4-η7-C(H)C(H)CC(H)C(H)C(H)C(H)], 4 and Ru4(CO)11(μ4-η2-HCCH)Ru(CO)3(μ-η1-η5-C5H4), 5. Compounds 2 and 3 were formed by opening of the Ru5 cluster of 1, the addition of three equivalents of C2H2, two of which became coupled to each other and to the carbido ligand of 1 to form bridging CC(H)C(H)C(H)C(H), pentadienyl ligands. Compounds 2 and 3 also contain a quadruply-bridging a η2-HCCH ligand. Compound 4 contains an open Ru5 cluster, in which three equivalents of C2H2 were coupled to each other and to the carbido ligand of 1 to form a quadruply-bridging heptadienyl η7-C(H)C(H)CC(H)C(H)C(H)C(H) ligand. Compound 5 contains a butterfly-tetrahedral Ru4 cluster with a quadruply-bridging a η2-HCCH ligand and a Ru(CO)3(μ-η1-η5-C5H4) grouping containing a metalated-cyclopentadienyl ligand that is linked to one of the wing-tip Ru atoms of the Ru4 cluster. The metalated-cyclopentadienyl ligand in 5 is believed to have been formed by a cyclization of the bridging, CC(H)C(H)C(H)C(H), pentadienyl ligand in compound 2. All new compounds were characterized by single-crystal X-ray diffraction analyses.

H2O adsorption and O-H breaking on Co5M (M = Co, Y-Ag) clusters: A DFT study

Interactions of H2O and metal clusters are of fundamental interest for several catalytic reactions. The adsorption and dissociation of H2O on Co5M clusters (M = Co, Y-Ag) were investigated with the density functional theory (DFT) method. The doping of Y, Zr, Nb, and Mo atoms in Co5M clusters not only enhances the adsorption strength for H2O but also decreases the barriers of O-H bond breaking, which is in the range of 0.17–0.36 eV. Therefore, the catalysis activity of the small cobalt clusters for H2O splitting can be optimized by doping heteroatoms. Molecular electrostatic potential (MESP) and overlaps partial density of states (OPDOS), and quantum theory of atoms in molecules (QTAIM) were employed for understanding the interaction characteristics.

INFLUENCE OF Sn ON THE MICROSTRUCTURE AND MECHANICAL PROPERTIES OF Ti-Mo-Nb ALLOYS FOR ORTHOPAEDIC APPLICATIONS

Metastable ß-Ti alloys intended for orthopaedic implants typically possess undesirable α′, α″, ω precipitates, which increase the elastic modulus. Non-toxic Sn was reported as an effective suppressor of α′, α″ and ω precipitates. Furthermore, increasing Sn content was reported to decrease the elastic modulus. In this study, the cluster plus glue atom (CPGA) model was used to develop structurally stable ß-Ti alloys through the addition of Sn. Arc melting was conducted to fabricate the alloys. The effect of substituting Mo atoms with 0.4 and 0.5 Sn atoms on the microstructure and mechanical properties of [(Mo,Sn)(Ti)14](Nb)1 alloys was investigated. The microstructure of the alloys exhibited large equiaxed beta grains with the [(Mo0.6Sn0.4)(Ti)14](Nb)1 and [(Mo0.5Sn0.5)(Ti)14](Nb)1 alloys showing substructures. The XRD results showed that the alloys consisted of the β phase; however, the presence of α” was observed in the [(Mo0.6Sn0.4)(Ti)14](Nb)1 alloy. The study showed that substitution of 0.5 Mo atoms with 0.5 atoms of Sn to form the [(Mo0.5Sn0.5)(Ti)14](Nb)1 cluster resulted in an elastic modulus of 49 GPa.

Enhancement of chemically bound gold recovery in post-activation heap leaching of refractory ore

This article discusses the main problems connected with heap leaching of chemically bound gold during mining refractory complex ores. It is proposed to prepare refractory ores for heap leaching by electrochemical and photochemical activation of solutions of oxidizing and complexing reagents. The composition of solutions is determined by the mineral composition of the ores. Dispersed and chemically bound gold can occur in various forms in the ores of the sulfide, sulfide–carbonaceous and sulfide–quartz genesis. Therefore, various oxidizing agents should be used when preparing ores for heap leaching. Oxidizing agents actively interact with ore-forming elements that have direct or indirect chemical bonds with clustered gold atoms. Depending on the modes of occurrence of chemically bound dispersed gold, governed by its geochemical associations with the ore-forming minerals, it is proposed to carry out oxidative preparation of refractory ores both at the stage of blasting operations and during pelletizing (agglomeration). Oxidative preparation is implemented with electro-photo-activated solutions with hydroxide-peroxide, sulfuric acid-peroxide, carbonateperoxide, hydroxychloride, sulfuric acid-nitrite-nitrate base. Direct heap leaching of chemically bound gold is proposed to carry out after oxidative treatment with activated solutions. The oxidative treatment includes irrigation of mineral piles with concentrated activated solutions and, then with electrochemically treated water or activated weakly concentrated solution of a complexing agent. Commercial-scale application of heap leaching with oxidation pre-activation in gold ore mining can enable efficient concentration of low-grade difficult ore. In this case, depending on mineral paragenesis of ore and geochemical association of disperse gold, the proposed post-activation heap leaching technology can use process solutions composed of different reagents both at the stage of blasting and during irrigation or pelletizing.

Solvothermal Synthesis of [Cr7 S8 (en)8 Cl2 ]Cl3 ⋅ 2H2 O with Magnetically Frustrated [Cr7 S8 ]5+ Double-Cubes.

A novel transition metal chalcohalide [Cr7S8(en)8Cl2]Cl3 ⋅ 2H2O, with [Cr7S8]5+ dicubane cationic clusters, has been synthesized by a low temperature solvothermal method, using dimethyl sulfoxide (DMSO) and ethylenediamine (en) solvents. Ethylenediamine ligand exhibits bi‐ and monodentate coordination modes; in the latter case ethylenediamine coordinates to Cr atoms of adjacent clusters, giving rise to a 2D polymeric structure. Although magnetic susceptibility shows no magnetic ordering down to 1.8 K, a highly negative Weiss constant, θ=−224(2) K, obtained from Curie‐Weiss fit of inverse susceptibility, suggests strong antiferromagnetic (AFM) interactions between S=3/2 Cr(III) centers. Due to the complexity of the system with (2S+1)7=16384 microstates from seven Cr3+ centers, a simplified model with only two exchange constants was used for simulations. Density‐functional theory (DFT) calculations yielded the two exchange constants to be J 1=−21.4 cm−1 and J 2=−30.2 cm−1, confirming competing AFM coupling between the shared Cr3+ center and the peripheral Cr3+ ions of the dicubane cluster. The best simulation of the experimental data was obtained with J 1=−20.0 cm−1 and J 2=−21.0 cm−1, in agreement with the slightly stronger AFM exchange within the triangles of the peripheral Cr3+ ions as compared to the AFM exchange between the central and peripheral Cr3+ ions. This compound is proposed as a synthon towards magnetically frustrated systems assembled by linking dicubane transition metal‐chalcogenide clusters into polymeric networks.

The role of silicon on solute clustering and embrittlement in highly neutron-irradiated pressurized water reactor surveillance test specimens

• The role of Si content on irradiation embrittlement was clarified. • Solute atom clusters of highly neutron-irradiated Japanese pressurized water reactor surveillance test specimens were analyzed by atom probe tomography. • The cluster radius and number density decreased and increased, respectively, with increasing Si content, resulting in a constant volume fraction of SCs. • Increase in Si reduces the degree of irradiation embrittlement. This is consistent with the results of our previous study based on Bayesian statistical analysis. Solute clusters (SCs) formed in pressurized water reactor surveillance test specimens neutron-irradiated to a fluence of 1 × 10 20 n/cm 2 were analyzed via atom probe tomography to understand the effect of silicon on solute clustering and irradiation embrittlement of reactor pressure vessel steels. In high-Cu bearing materials, Cu atoms were aggregated at the center of cluster surrounded by the Mn, Ni, and Si atoms like a core-shell structure. In low-Cu bearing materials, Mn, Ni, and Si atoms formed cluster and these solutes were not comprised core-shell structure in SCs. While the number of Cu atoms in clusters was decreased with decreasing nominal Cu content, the number of Si atoms had clearly increased. The cluster radius ( r ) and number density ( N d ) decreased and increased with increasing nominal Si content, respectively. The shift in the reference temperature for nil-ductility transition ( ΔRT NDT ) showed a good correlation with the square root of volume fraction ( V f ) multiplied by ( V f × r ) . The negative relation between the nominal Si content and ΔRT NDT indicated that increasing of nominal Si content reduces the degree of embrittlement.

Exploring the Effects of a Doping Silver Atom on Anionic Gold Clusters' Reactivity with O2.

Reactivities of AgAun-1- (n = 3-10) with O2 at a low temperature were studied using an instrument combining a magnetron sputter cluster source, a microflow reactor, and a time-of-flight mass spectrometer. Their reaction products as well as size-dependent kinetic rates were nearly identical to those of corresponding Aun- (n = 3-10). Previous experiments showed that the Ag atom in AgAun-1- (n = 3-10) was fully or partially enclosed by the gold atoms. We studied the adsorption of O2 on these reported structures using the B3LYP theory with relatively large basis sets. The theoretical results indicate that the adsorption sites as well as the adsorption energies of O2 on AgAun-1- (n = 3-10) are nearly identical to those on the corresponding Aun- (n = 3-10). The O2 adsorption on a series of proposed isomers of AgAun-1- (denoted as Aun-1Ag-), in which the silver atom was on the protruding site, was explored using the same theoretical methods. The O2 tends to bond with the protruding Ag atoms, and the binding energies are apparently higher than those on the corresponding Aun- and AgAun-1-. The adsorption and activation of O2 on Aun-, AgAun-1-, and Aun-1Ag- were correlated with their global electron detachment energies (VDEs) as well as the element types of the adsorption sites. Generally, low VDE values and silver sites facilitate the O2 adsorption, and these two factors separately dominate in various cluster species. The revealed effects of a doping silver atom in small gold clusters are helpful to understand the role of the residual silver components in many nano gold catalysts.

First-principles study of helium-vacancy complexes in Be12Ti

First-principles calculations have been conducted to study the stability of He-vacancy clusters and the trapping behavior of vacancies for He atoms in Be12Ti. We considered the various metastable microstructures of four types of He-vacancy clusters, and the most stable configurations were determined by the calculations of solution energy. Some He-vacancy clusters in Be12Ti have specific geometrical shape, and grow along specific crystal plane. For example, three types of He2V clusters (two He atoms trapped by vacancy) form dumbbell-shaped structure, three He atoms of He3V clusters (three He atoms trapped by vacancy) are located in the specific crystal plane. The solution energies of four types of clusters increase with the increase of number of He atoms, and the increasing rate is basically identical. The solution energies of HenVBe1 clusters are always the largest, and the solution energies of the HenVTi clusters are always the smallest, which mainly attribute to the larger vacancy volume and perfect spatial symmetry of Ti vacancies. The binding energies of a single He atom with HenV (n=0-3) clusters are all positive, and the segregation of He atoms on the inner surface of the vacancy is closer to the center of the vacancy, indicating that the He-vacancy has a stronger trapping ability for He atoms. The present research results provide a theoretical foundation of vacancy trapping mechanism for He atoms in Be12Ti, which is extremely important for the nucleation and growth mechanism of He bubbles in Be12Ti.

Theoretical comparative survey on the structure and electronic properties of first row transition metal substituted Keggin type polyoxometalates

In the present study, molecular geometry, electronic structure, first row transition metal-polyoxometalate interactions, transition metal-H2O bonding, and simulated infrared (IR) spectrum of H2O ligated/unligated transition metal substituted Keggin type polyoxometalates ([PW11O39(MII/MIIOH2)]5-, MII ​= ​Cr, Mn, Fe, Co, Ni, Cu and Zn) have been studied through Density Functional Theory (DFT) calculations. From the results, it has been predicted that the interaction of H2O ligand with MII leads to a stable [PW11O39(MII-H2O)]5- complex, without spin crossing during water attachment. The calculations have also revealed that interaction of H2O ligand with [PW11O39(MII)]5- could be discussed in two different classes: when MII is Cr, Mn and Fe, the H2O molecule interacts directly to MII from O side, while for MII ​= ​Co, Ni, Cu and Zn, the H-bond interaction between H2O and O atoms around the M, leads to the stabilization of POM-H2O system. Moreover, it has been predicted that the binding properties of H2O strikingly depends on axial 3dz2 orbital of MII. In this regard, it has been exhibited that the affinity of H2O for MII in [PW11O39(MII)]5- with a filled 3dz2 orbital, is strongly reduced as measured by increasing in calculated MII-ligand distance. Also, strong contributions of MII 3d as well as the 2p orbitals of five oxygen donor atoms in polyoxometalate cluster results in the bonding interaction between MII and lacunary Keggin polyoxometalate. The DFT-derived IR spectra showed displacement and splitting in four previously known vibrational bands of Keggin-type polyoxometalate, α-[PW12O40]3-, owing to transition metal substitution and H2O ligation.

Magic Numbers in Boson 4He Clusters: The Auger Evaporation Mechanism.

The absence of magic numbers in bosonic 4He clusters predicted by all theories since 1984 has been challenged by high-resolution matter-wave diffraction experiments. The observed magic numbers were explained in terms of enhanced growth rates of specific cluster sizes for which an additional excitation level calculated by diffusion Monte Carlo is stabilized. The present theoretical study provides an alternative explanation based on a simple independent particle model of the He clusters. Collisions between cluster atoms in excited states within the cluster lead to selective evaporation via an Auger process. The calculated magic numbers as well as the shape of the number distributions are in quite reasonable agreement with the experiments.

Benzene-1,3-disulfonate capped gold nanoparticles: DFT computations in support of particles-capping agent and nano-sensing interactions

We have successfully synthesized water-dispersible gold (Au) nanoparticles (NPs) using benzene disulfonate anions (BDS2−) as a capping agent and applied them for the colorimetric recognition of Pb2+ and Cu2+ ions in aqueous solutions. The synthetic method for the BDS-AuNPs is very simple, one-pot and rapid. The particles are stable in a wide pH range of 5 to 10 over a month and are small in size (dTEM=8.9nm and dDLS=17nm). They selectively bind Pb2+ and Cu2+ ions over 14 other metal ions. This makes the particles an efficient optical dual-nanosensor. The limit of detection (LOD) values for Pb2+(0.469 μM) and Cu2+ (0.645 μM) ions are quite low. The association constant values for the Pb2+----BDS-AuNPs and Cu2+-----BDS-AuNPs complexes are found to be 1.612 × 106 M−1 (R2 adj. 0.9603) and 8.12 × 105 M−1 (R2 adj 0.9947), respectively, indicating strong interactions between the particles and the metal ions. A DFT computational study reveals that the binding affinity of BDS to the Aun cluster increases with the increase of Au atoms in the Aun cluster, supporting the experimental findings. The practical acceptance of the sensor was tested with real samples, where the sensor showed excellent recovery results. So, the BDS-AuNPs could be treated as an easy-to-develop dual-nanosensor for Pb2+ and Cu2+ metal ions.

Efficiency in identification of internal structure in simulated monoatomic clusters: Comparison between common neighbor analysis and coordination polyhedron method

Efficiency of two methods for structural analysis, the Common Neighbor Analysis (CNA) from the program OVITO and the Coordination Polyhedron Method (CPM), was compared when applied to detect all possible structural atoms in monoatomic test clusters. The analyzed clusters are in the form of spherical fragments of a pure or disturbed crystal structure or they represent Mackay icosahedra. It was observed that the number of detected structural atoms for both methods is initially similar but decreases rapidly with the increase of applied random translations of atoms. CNA gives higher number of detected structural atoms representing bulk-centered cubic structure, while CPM has significant advantage in detection of icosahedral units. CNA is unable to identify decahedral units; therefore, this method fails to visualize clearly any global symmetry in internal cluster structure. Attempts are made to understand the reasons for the poor performance of both methods in the mentioned aspects and some ways are proposed to improve them.