Cn Clusters Research Articles

Unveiling Carbon Cluster Coating in Graphene CVD on MgO: Combining Machine Learning Force field and DFT Modeling.

In this study, we investigate the behavior of carbon clusters (Cn, where n ranges from 16 to 26) supported on the surface of MgO. We consider the impact of doping with common impurities (such as Si, Mn, Ca, Fe, and Al) that are typically found in ores. Our approach combines density functional theory calculations with machine learning force field molecular dynamics simulations. It is found that the C21 cluster, featuring a core-shell structure composed of three pentagons isolated by three hexagons, demonstrates exceptional stability on the MgO surface and behaves as an "enhanced binding agent" on MgO-doped surfaces. The molecular dynamics trajectories reveal that the stable C21 coating on the MgO surface exhibits less mobility compared to other sizes Cn clusters and the flexible graphene layer on MgO. Furthermore, this stability persists even at temperatures up to 1100K. The analysis of the electron localization function and potential function of Cn on MgO reveals the high localization electron density between the central carbon of the C21 ring and the MgO surface. This work proposes that the C21 island serves as a superstable and less mobile precursor coating on MgO surfaces. This explanation sheds light on the experimental defects observed in graphene products, which can be attributed to the reduced mobility of carbon islands on a substrate that remains frozen and unchanged.

A Low-Order Permutationally Invariant Polynomial Approach to Learning Potential Energy Surfaces Using the Bond-Order Charge-Density Matrix: Application to Cn Clusters for n = 3-10, 20.

A representation for learning potential energy surfaces (PESs) in terms of permutationally invariant polynomials (PIPs) using the Hartree-Fock expression for electronic energy is proposed. Our approach is based on the one-electron core Hamiltonian weighted by the configuration-dependent elements of the bond-order charge density matrix (CDM). While the previously reported model used an s-function Gaussian basis for the CDM, the present formulation is expanded with p-functions, which are crucial for describing chemical bonding. Detailed results are demonstrated on linear and cyclic Cn clusters (n = 3-10) trained on extensive B3LYP/aug-cc-pVTZ data. The described method facilitates PES learning by reducing the root mean squared error (RMSE) by a factor of 5 relative to the s-function formulation and by a factor of 20 relative to the conventional PIP approach. This is equivalent to using CDM and an sp basis with a PIP of order M to achieve the same RMSE as with the conventional method with a PIP of order M + 2. Implications for large-scale problems are discussed using the case of the PES of the C20 fullerene in full permutational symmetry.

Amyloid and Tau Predominance Subtyping Identifies CI Patients With Different Clinical Phenotypes

AbstractBackgroundThe ATN classification system assumes a sequential model of disease progression. However, there are groups of individuals in the same ATN category that exhibit a predominance of abnormality (higher burden) of one of the biomarkers, creating heterogeneous ATN groups regarding pathological predominance. Thus, we tested the hypothesis that individuals clustered by ATN biomarker abnormality predominance may offer an alternative to groups defined using biomarkers cut‐offs.MethodWe assessed 103 cognitively impaired individuals(CDR> = 0.5) from the TRIAD cohort with available measures of plasma phosphorylated tau‐181, brain MRI, amyloid PET, and tau PET. We used the K‐means algorithm to stratify participants into three clusters. We compared the clusters on composite measures of memory, executive functioning, language, and visuospatial processing. To examine the utility of the discovered clusters, we compared them to traditional ATN categories in the prediction of neuropsychological measures. We did so by creating three categories: patients positive on all three ATN biomarkers, patients positive on two of the three biomarkers, and patients positive on either one or none. Additionally, we created an inflammation, amyloid and tau deposition probabilistic map anchored on young controls(n = 51, mean age = 23.74).ResultsWe uncovered 3 clusters: an amyloid predominant (AP) cluster, a tau/phosphor‐tau predominant cluster (TP), and a cluster showing no predominance with low levels on all biomarkers (CN)(figure 1). Notably, levels of neurodegeneration and inflammation were similar between the AP and TP clusters. The AP cluster significantly differed from the CN cluster in memory only. Participants in the TP cluster had significantly lower scores in memory, executive functioning, language, and visuospatial processing than the other two clusters. In comparison, using threshold‐based ATN groups showed milder differences in memory and executive functioning, and no differences in language and visuospatial processing(figure 2). Furthermore, cluster membership moderated the relationship between various biomarkers, to the point of reversing the direction of correlation(figure 3).ConclusionOur results highlight the biological heterogeneity present within the Alzheimer’s disease continuum and that the pathological predominance of amyloid and tau is associated with different disease phenotypes. Approaching dementia patients with an eye on the predominance of pathology rather than cutoffs for abnormality may provide a better understanding of AD pathological subtypes.

Amyloid and Tau Predominance Subtyping Identifies CI Patients With Different Clinical Phenotypes

AbstractBackgroundThe ATN classification system assumes a sequential model of disease progression. However, there are groups of individuals in the same ATN category that exhibit a predominance of abnormality (higher burden) of one of the biomarkers, creating heterogeneous ATN groups regarding pathological predominance. Thus, we tested the hypothesis that individuals clustered by ATN biomarker abnormality predominance may offer an alternative to groups defined using biomarkers cut‐offs.MethodWe assessed 103 cognitively impaired individuals(CDR> = 0.5) from the TRIAD cohort with available measures of plasma phosphorylated tau‐181, brain MRI, amyloid PET, and tau PET. We used the K‐means algorithm to stratify participants into three clusters. We compared the clusters on composite measures of memory, executive functioning, language, and visuospatial processing. To examine the utility of the discovered clusters, we compared them to traditional ATN categories in the prediction of neuropsychological measures. We did so by creating three categories: patients positive on all three ATN biomarkers, patients positive on two of the three biomarkers, and patients positive on either one or none. Additionally, we created an inflammation, amyloid and tau deposition probabilistic map anchored on young controls(n = 51, mean age = 23.74).ResultWe uncovered 3 clusters: an amyloid predominant (AP) cluster, a tau/phosphor‐tau predominant cluster (TP), and a cluster showing no predominance with low levels on all biomarkers (CN)(figure 1). Notably, levels of neurodegeneration and inflammation were similar between the AP and TP clusters. The AP cluster significantly differed from the CN cluster in memory only. Participants in the TP cluster had significantly lower scores in memory, executive functioning, language, and visuospatial processing than the other two clusters. In comparison, using threshold‐based ATN groups showed milder differences in memory and executive functioning, and no differences in language and visuospatial processing(figure 2). Furthermore, cluster membership moderated the relationship between various biomarkers, to the point of reversing the direction of correlation(figure 3).ConclusionOur results highlight the biological heterogeneity present within the Alzheimer’s disease continuum and that the pathological predominance of amyloid and tau is associated with different disease phenotypes. Approaching dementia patients with an eye on the predominance of pathology rather than cutoffs for abnormality may provide a better understanding of AD pathological subtypes.

Characterization of thermal decomposition mechanism and combustion performance of 4,4’‐azobis(1,2,4‐triazole)**

Abstract4,4’‐azobis(1,2,4‐triazole) (ATRZ), as a representative of high‐nitrogen compound, has attracted extensive interests. This work explores the thermal decomposition mechanism and combustion performance of ATRZ. The thermogravimetry‐differential scanning calorimetry‐fourier transform infrared spectroscopy (TG‐DSC‐FTIR) of ATRZ was carried out at heating rate of 10 °C/min in an argon atmosphere. ATRZ has two peak exothermic temperatures, 110.24 °C and 306.85 °C respectively. The exothermic peak at 110.24 °C is the decomposition of ATRZ tiny debris, and the exothermic peak at 306.85 °C is the decomposition of the main part of ATRZ. The pyrolysis‐gas chromatography mass spectrometry (PY‐GC/MS) of ATRZ was carried out at 350 °C in an argon atmosphere. By combining TG‐DSC‐FTIR and PY‐GC/MS, the thermal decomposition mechanism of ATRZ was speculated. The main reaction in the ATRZ pyrolysis process is the cleavage of two N−N single bonds in the nitrogen bridge, forming a nitrogen molecule and two triazole rings, which is the majority of the first step decomposition reaction. At the same time, a small number of triazole rings break off to form other intermediates. A small amount of nitrogen gas is generated and a large number of CN clusters are formed. Under the same testing conditions, ATRZ has a higher combustion heat (19318 J/g) than other traditional CHNO energetic materials. By comparing the laser ignition combustion of ATRZ and ATRZ+RDX, the combustion temperature of ATRZ+RDX is higher and the combustion duration is longer. The introduction of CHNO type ammonium nitrate explosives promotes the energy release of ATRZ.

A simultaneous dual-polarity mass spectrometer with electron start for MeV-SIMS

The Capillary Heavy Ion MeV-SIMS Probe (CHIMP) at ETH Zürich has been redesigned with a second mass spectrometer and symmetric extraction to enable simultaneous analysis of positive and negative secondary ions. Secondary electrons are deflected within the negative spectrometer and detected independently. The fast secondary electron signal is used as a start signal for both Time-of-Flight mass spectrometers.The new setup enables the simultaneous acquisition and analysis of both secondary ion polarities emitted under identical conditions from the same sample location. This allows to study correlations between secondary ions of different polarities emitted from a single primary ion impact. Measurements with small primary Cn cluster ions show the influence of cluster size on the multiplicity of secondary ion emission. Furthermore, a cluster effect in the ratio between positive and negative ion yields of corresponding secondary ion species is identified, with the ratio approaching parity for larger cluster sizes n.

Differential gain of chromosomal regions 20q or 13q with loss of 8p and 18q differentiates disease-free survival in colorectal cancer.

126 Background: In microsatellite stable (MSS) colorectal cancer (CRC) cases, frequent amplifications in 13q and 20q regions have been reported with limited understanding of their potential role for prognosis and treatment. Based on an internal research molecular tumor board case analysis of a KRAS WT, MSS left-sided (LS), metastatic CRC patient, we noted 50% of the 11 listed variants of unknown significance were on 20q. This study aims to investigate the potential prognostic role for gain of 20q chromosomal regions relative to other chromosomal imbalances using a retrospective cohort. Methods: We performed a genome-wide CN cluster analysis using the TCGA data with resulting patient clusters compared based on Kaplan-Meier estimated disease-free interval (DFI) in months (mos) using a log-rank. We examined associations between CN-derived clusters and CRC phenotypes. Results: Using TCGA data, we identified four CN-derived patient clusters of which two had significantly different DFI’s. One longer DFI cluster (n = 83; median DFI = 28mos) was defined by a signature of copy neutral genes along Chr8p and 18q regions. The shorter DFI cluster (n = 46; median DFI = 20mos) was defined by a signature of Chr8p and 18q regions of loss. The two clusters significantly differed in terms of site (85% right-sided in the shorter vs. 85% LS in the longer DFI cluster) and MS status (81% MSS in the shorter vs. 72% MSI in the longer DFI cluster) with no significant differences in age (mean of 70 years at diagnosis) and KRAS status (around 50% WT) between clusters. The shorter DFI was able to be further differentiated based on gain of chromosomal regions 20q (n = 26; median DFI = 24mos) and 13q (n = 20; median DFI = 18mos). No significant differences in mean age, tumor stage, site, and MS status between the shorter DFI subgroups were noted. Enriched pathways in the Chr20q gain sub-cluster include cell differentiation (Hippo, Rap1, VEGF), whereas metabolic signaling pathways via AGE-RAGE and AMPK, as well as cell growth and malignant transformation via RAS are enriched in the Chr13q gain sub-cluster. Conclusions: Clinical sequencing is able to identify regions of gain in Chr20q and Chr13q as part of VUS’s. Gain of Chr20q has been reported with better survival in mCRC patients. Gain of chromosomal region 20q and loss of 18q has been reported to discriminate between Lynch Syndrome and familial colorectal cancer. Herein, we show that gain of the 20q region with 18q and 8p regions of loss is associated with shorter DFI and gain of 13q region with loss of 8p even worse prognosis.

Electron-loss and destruction processes in collision of MeV/atom carbon cluster ions with rare gases

Singly charged cluster-ion yield ϕ1 of MeV/atom carbon cluster ions, generated using He and Ne gases as a charge-changing gas in tandem accelerator, is analytically formulated by six cross sections on the basis of the rate equation. These cross sections for electron-loss process from a cluster were estimated with use of the time-dependent quantum theory, assuming binary collision treatment and independent electron model. The cross sections in ϕ1 estimated for MeV/atom Cn (n = 2–4) clusters were found to show the sub-linear dependence on the atom number n. The gas-pressure dependences of the ϕ1 values calculated for the 2.5 MeV C2+ and C4+ ions using Ne gas are in good agreement with the experimental data obtained at TIARA.

Modified Particle Swarm Optimization Algorithms for the Generation of Stable Structures of Carbon Clusters, Cn (n = 3-6, 10).

Particle Swarm Optimization (PSO), a population based technique for stochastic search in a multidimensional space, has so far been employed successfully for solving a variety of optimization problems including many multifaceted problems, where other popular methods like steepest descent, gradient descent, conjugate gradient, Newton method, etc. do not give satisfactory results. Herein, we propose a modified PSO algorithm for unbiased global minima search by integrating with density functional theory which turns out to be superior to the other evolutionary methods such as simulated annealing, basin hopping and genetic algorithm. The present PSO code combines evolutionary algorithm with a variational optimization technique through interfacing of PSO with the Gaussian software, where the latter is used for single point energy calculation in each iteration step of PSO. Pure carbon and carbon containing systems have been of great interest for several decades due to their important role in the evolution of life as well as wide applications in various research fields. Our study shows how arbitrary and randomly generated small Cn clusters (n = 3–6, 10) can be transformed into the corresponding global minimum structure. The detailed results signify that the proposed technique is quite promising in finding the best global solution for small population size clusters.

Fully versus constrained statistical fragmentation of carbon clusters and their heteronuclear derivatives.

The Microcanonical Metropolis Monte Carlo (MMMC) method has been shown to describe reasonably well fragmentation of clusters composed of identical atomic species. However, this is not so clear in the case of heteronuclear clusters as some regions of phase space might be inaccessible due to the different mobility of the different atomic species, the existence of large isomerization barriers, or the quite different chemical nature of the possible intermediate species. In this paper, we introduce a constrained statistical model that extends the range of applicability of the MMMC method to such mixed clusters. The method is applied to describe fragmentation of isolated clusters with high, moderate, and no heteronuclear character, namely, CnHm, CnN, and Cn clusters for which experimental fragmentation branching ratios are available in the literature. We show that the constrained statistical model describes fairly well fragmentation of CnHm clusters in contrast with the poor description provided by the fully statistical model. The latter model, however, works pretty well for both Cn and CnN clusters, thus showing that the ultimate reason for this discrepancy is the inability of the MMMC method to selectively explore the whole phase space. This conclusion has driven us to predict the fragmentation patterns of the C4N cluster for which experiments are not yet available.

Possible lower energy isomer of carbon clusters Cn (n = 11, 12) via particle swarm optimization algorithm: Ab initio investigation

The low energy structures of neutral carbon clusters Cn (n = 11, 12) are predicted by means of particle swarm optimization and quantum chemistry calculation. The energy and geometrical structure of these isomers are further optimized by DFT, MP2 and CCSD computation methods. The relative Gibbs free energy below 5000 K was calculated, which indicates that C11 clusters are more sensitive to temperature. We also illustrate the computational simulated IR spectra obtained at B3LYP/cc-pVTZ level, which shown the vibrational modes and vibrational regions of different structural isomers. Combining nuclear independent chemical shift (NICS) and harmonic oscillator measure of aromaticity (HOMA), we have analyzed the aromaticity of the three single-ring structures and found that C11 cluster is not aromatic, while the ground stated structure of C12 is anti-aromaticity. Chemical bond analysis of the ground state is performed by Adaptive Natural Density Partition (AdNDP) injunction with electron localization function (ELF), it is found that the 2c-2e bonds of C11 and C12 planar ring structures presented strong and weak alternations, respectively, and their multi-central bonds were strongly dependent on the symmetry of molecular configuration. Finally, topological and natural bond orbital (NBO) analysis indicate that there is no electrostatic interaction in the Cn (n = 11, 12) clusters, and the high angular momentum orbital has a primary contribution to negative natural valance electron configuration. From the electronic configuration, we can see that the natural hybridized orbit of C11 and C12 clusters is mainly composed of sp hybrids.

Li-Decorated Fullerenes: A DFT Study

Density functional calculations have been applied to study the structure, stability and aromaticity of Li-decorated non-IPR fullerene cages, Cn with n = 44, 46, 48, and 50, and IPR fullerene cages, Cn with n = 60, 70, 76, and 84. Based on our results, the binding energies per Li atom for Li12Cn clusters depend on the type and size of the cages. As of Li-decorated IPR fullerenes, where pentagons are isolated, there is virtually no interaction between the Li atoms, so that the binding energies for the Li-decorated IPR Cn fullerenes are obtained to be larger than those for the Li-decorated non-IPR ones. The C–C bond lengths in the pentagons of Li12Cn clusters are enlarged relative to those of pristine Cn clusters. Based on NBO analysis, charge transfer (~ 0.5e) from Li to the fullerene cage makes the Li atoms positively charged. NICS data suggest that the degree of aromaticity in C60, C76, and C84 cages increases upon formation of the Li-decorated Cn clusters while more positive NICS values are obtained for C70 and the smaller fullerenes with Li decoration of the cages.

First-Principles Investigations of Dimetallic Carbide Clusters: Bi2Cn (n = 1–16)

The geometries, electronic and magnetic properties of Bi2Cn (n = 1–16) clusters have been systematically studied using density functional theory. The results show that Bi2Cn (n = 1–16) clusters prefer linear structures with the two Bi atoms at the two ends of a linear Cn cluster. We predict that the magic number of Bi2Cn (n = 1–16) clusters should be 4, 6, 8, 11, 13, and 15. According to the Mulliken population analysis, charges always transfer from Bi atoms to C atoms. The total magnetic moment is completely quenched for the Bi2Cn clusters with even n while the odd structures carry a magnetic moment of 2μB, suggesting that the addition of one Bi atom to small BiCn clusters have played an important role in tailoring the host’s magnetism, which will likely have potential applications in new nanomaterials with tunable magnetic properties.

Theoretical study of electron transport properties of SimCn /Cn clusters tethered on graphene nanoribbon

Electron transport properties of optimized typical SimCn/Cn clusters, including Si4C, Si8C5, Si9C6, C6, C12 and C13, connected to zigzag graphene nanoribbon (ZGNR) electrodes are theoretically studied through first-principles density functional theory (DFT). As for Si4C, Si8C5, Si9C6 clusters, the transmission values at the fermi level show a decreasing tendency with the increase in the number of carbon and silicon atoms. Interestingly, Si9C6 cluster with ring structure (C6) has poor electron transport properties in spite of C6 showing good electron transport properties. Although C12 cluster shows smaller transmission values at the fermi level, when adding an atom to it, - C13 shows excellent electron transport properties. The electrode coupling of ZGNR-C12 is the strongest compared with ZGNR-C6 and ZGNR-C13 because it forms sp3 orbital which has stronger bond. Our findings may pave a new path for the exploration of nano electronics.

Ion velocities of laser desorbed ions passing through quadrupole electric fields

This paper is a study of the effects of quadrupole electric fields on the velocities of ions generated by laser desorption ionization (LDI). We used a charge detector to measure ion flight time in the absence of electric and magnetic fields to obtain the initial velocity distribution of ions generated in the LDI process. It was found that the measured ion velocity of fullerene and matrix ions was proportional to the energy of the laser pulse. Then we measured velocity distributions of fullerene ions in rf-only quadrupoles. It was observed that the electric field in the fringing field region was proportional to pseudo-potential well depth (Dz) and that ions gained velocity in the fringing field region and speeded up as the Dz was increased due to transfer of rotational energy into translational energy in the high-order field region. Initial velocity of ions passing through different stages of quadruple was increased at every stage. In addition, the mass spectrometric analysis showed when the rf amplitude was low, the quadrupole field allowed stable motion of low mass ions; when the rf amplitude was increased, effective potential well depth was reduced. This is evident that the gradient of ion velocity drops as the difference in Dz increases for C60 and high mass Cn cluster ions.

Structural surface elements of diamond-core nanoparticles

Ab initio modeling of Cn clusters comprising up to 250 atoms and having a diamond core revealed stable primary surface elements of nondiamond nature. At large local curvature of the surface, pentaatomic rings dominate. At a smaller local curvature, the fraction of six-membered rings increases, and so does the fraction of structures that resemble open fragments of fullerenes and nuclei of cross-sectional segments of nanotubes.

First-principles study of structural and electronic properties of carbon clusters

Using a first-principles method based on density functional theory, together with the generalised gradient approximation, the structures and electronic properties of Cn(n = 2–9) clusters have been determined, and their highest occupied molecular orbital–lowest unoccupied molecular orbital energy gaps and their binding energies have been calculated. The results show that the Cn cluster binding energy, and therefore, the stability of the cluster structure increase monotonically with cluster size n. The cluster energy gap varies in a non-monotonic manner with cluster size, and its range of values indicates that the clusters behave as semiconductors. According to the partial density of states of the carbon atoms, the energy of the s state falls with increasing cluster size, whereas the energy of the p state rises.

Geometry, vibrational frequency, and isomerization of neutral and cation Cu–CN complex

The geometry structure, vibrational frequency, and the isomerization of neutral and cation copper cyanide systems ( CuCN and CuCN +) were investigated by employing three DFT methods (B3LYP, B3P86 and B3PW91) and MP2 functional with 6-311+G* basis set. The cyanides CuCN (1Σ+) is the most stable one among the isomers of CuCN , and CuNC +(2Σ+) isocyanides is the global minimum on its potential energy surface (PES). The vibrational modes of these isomers were assigned. Two dissociation mechanisms were designed for each species. The complex ( CuCN and CuCN +) tends to dissociate through neutral mechanism into CN cluster. The useful information is brought forward about the synthesis of material and biological macromolecule. The state–state isomerization pathways were established using the intrinsic reaction coordinate (IRC).

Photocurrent responsive properties of a series of charge-transfer materials with nano-sized CdS/Se clusters and ruthenium complex dyes

Large cadmium chalcogenido clusters C2 (Cd32) and C1 (Cd17) CdQ (Q = S, Se) with photoactive dye cations [Ru(Phen/Bpy)3]2+ are prepared under solvothermal conditions (Phen = 1,10-phenanthroline, Bpy = 2,2′-bipyridine). All the C2 compounds are 3-D polymeric structures, while the C1 compounds are discrete Cd17 clusters. Two of the 3-D C2 clusters can be considered as homosized nano CdSe@CdS core–shell particles (2.0 nm radius) with Cd4Se10 core. Charge-transfer interaction is found between [Ru(Phen/Bpy)3]2+ cations and CdQ cluster anions. The photocurrent behaviors indicate that (1) the current intensities are greatly increased for the dye cation functionalized Cn clusters, (2) the current intensities of the 3-D C2 clusters are larger than those of the discrete C1 clusters, and (3) the current intensities of the selenide clusters are larger than those of the sulfide clusters.

Investigation of ternary ConCN−1/0 (n = 1–5) clusters by density functional calculations

The neutral and anionic Co(n)CN (n = 1-5) clusters were investigated using density functional calculations. The most stable structures of neutral and anionic Co(n)CN (n = 1-5) clusters have been identified. In these structures, the CN radical retains its integrity as a structural unit. For anionic Co(n)CN(-) (n = 1-5) and neutral Co(n)CN (n = 1-2) clusters, the CN prefers to be adsorbed on the top sites of Co(n) clusters via the C terminal, forming a linear or quasi-linear N-C-Co structure. For neutral Co(n)CN (n = 3-5) clusters, the CN is adsorbed on the bridge sites of Co(n) (n = 3-5) by both C and N atoms. Compared to the free CN radical calculated at the same level, the C-N stretching frequencies of neutral Co(n)CN (n = 3-5) are red-shifted while they are blue-shifted for neutral Co(n)CN (n = 1-2). The adiabatic and vertical detachment energies of anionic Co(n)CN(-) (n = 1-5) clusters are calculated based on density functional calculations. In addition, the most favored dissociation channels of neutral and anionic Co(n)CN (n = 1-5) clusters are determined by calculating the dissociation energies of various possible dissociation pathways.