Number Of Atoms Research Articles

Comparative analysis of absorption resonances between carbynes and cyclo[n]carbons.

Two approaches are presented here to analyze the absorption resonances between carbynes and cyclo[n]carbons, namely the analytical tight-binding model to calculate the optical selection rules of cumulenic atomic rings and chains and theab initiotime-dependent density functional theory for the optical investigation of polyynic carbon ring and chains. The optical absorption spectra of the carbon ring match that of the finite chain when their eigen energies align following theNring= 2Nchain+ 2 rule, which states that the number of atoms in an atomic ringNringis twice the number of atoms on a finite chainNchainwith two additional atoms. Two representative atomic chains are chosen for our numerical calculations, specifically carbynes withN= 7 and 8 carbon atoms as optical resonance spectra match to a recently synthesized carbon ring called cyclo$[18]$carbon. Despite the mismatch in resonance peaks, molecular orbital transitions of both carbynesN= 7 and 8 and cyclo[n]carbons reveal a wave function symmetry change from inversion to reflection and vice versa for allowed molecular orbital transitions, which results in electron density redistribution along the polyynic carbyne axis or the cyclo[n]carbons circumference. Our investigation of the correlation of optical absorption peaks between carbynes and cyclo[n]carbons is a step towards enhancing the reliability of allotrope identification in advanced molecular device spectroscopy. Moreover, this work could facilitate the non-invasive, rapid and crucial assessment of these sensitive 1D allotropes by providing accurate descriptions of their electronic and optical properties, particularly in controlled synthesis environments.

Hydrogen production catalysed by atomically precise metal clusters.

Atomically precise metal clusters that possess the exact atom number, definitive composition, and tunable geometric and electronic structures have emerged as ideal model catalysts for many important chemical processes. Recently, metal clusters have been widely used as excellent catalysts for hydrogen production to explore the relationship between the structure and catalytic properties at the atomic level. In this review, we systematically summarize the significant developments concerning metal clusters as electrocatalysts and photocatalysts for hydrogen generation. This review also puts forward the challenges and perspectives of atomically precise metal clusters in electrocatalysis and photocatalysis in the hope of providing a valuable reference for the rational design of high-performance catalysts for hydrogen production.

Hexa‐atom Pt Catalyst Fabricated by a Ligand Engineering Strategy for Efficient Hydrogen Oxidation Reaction

Atomically precise supported nanocluster catalysts (APSNCs), which feature exact atomic composition, well‐defined structures, and unique catalytic properties, offer an exceptional platform for understanding the structure‐performance relationship at the atomic level. However, fabricating APSNCs with precisely controlled and uniform metal atom numbers, as well as maintaining a stable structure, remains a significant challenge due to uncontrollable dispersion and easy aggregation during synthetic and catalytic processes. Herein, we developed an effective ligand engineering strategy to construct a Pt6 nanocluster catalyst stabilized on oxidized carbon nanotubes (Pt6/OCNT). The structural analysis revealed that Pt6 nanoclusters in Pt6/OCNT were fully exposed and exhibited a planar structure. Furthermore, the obtained Pt6/OCNT exhibited outstanding acidic HOR performances with a high mass activity of 18.37 A·mgpt‐1 along with excellent stability during a 24 h constant operation and good CO tolerance, surpassing those of the commercial Pt/C. Density functional theory (DFT) calculations demonstrated that the unique geometric and electronic structures of Pt6 nanoclusters on OCNT altered the hydrogen adsorption energies on catalytic sites and thus lowered the HOR theoretical overpotential. This work presents a new prospect for designing and synthesizing advanced APSNCs for efficient energy electrocatalysis.

Hexa-atom Pt Catalyst Fabricated by a Ligand Engineering Strategy for Efficient Hydrogen Oxidation Reaction.

Atomically precise supported nanocluster catalysts (APSNCs), which feature exact atomic composition, well-defined structures, and unique catalytic properties, offer an exceptional platform for understanding the structure-performance relationship at the atomic level. However, fabricating APSNCs with precisely controlled and uniform metal atom numbers, as well as maintaining a stable structure, remains a significant challenge due to uncontrollable dispersion and easy aggregation during synthetic and catalytic processes. Herein, we developed an effective ligand engineering strategy to construct a Pt6 nanocluster catalyst stabilized on oxidized carbon nanotubes (Pt6/OCNT). The structural analysis revealed that Pt6 nanoclusters in Pt6/OCNT were fully exposed and exhibited a planar structure. Furthermore, the obtained Pt6/OCNT exhibited outstanding acidic HOR performances with a high mass activity of 18.37 A·mgpt-1 along with excellent stability during a 24 h constant operation and good CO tolerance, surpassing those of the commercial Pt/C. Density functional theory (DFT) calculations demonstrated that the unique geometric and electronic structures of Pt6 nanoclusters on OCNT altered the hydrogen adsorption energies on catalytic sites and thus lowered the HOR theoretical overpotential. This work presents a new prospect for designing and synthesizing advanced APSNCs for efficient energy electrocatalysis.

Dataset for quantum-mechanical exploration of conformers and solvent effects in large drug-like molecules

We here introduce the Aquamarine (AQM) dataset, an extensive quantum-mechanical (QM) dataset that contains the structural and electronic information of 59,783 low-and high-energy conformers of 1,653 molecules with a total number of atoms ranging from 2 to 92 (mean: 50.9), and containing up to 54 (mean: 28.2) non-hydrogen atoms. To gain insights into the solvent effects as well as collective dispersion interactions for drug-like molecules, we have performed QM calculations supplemented with a treatment of many-body dispersion (MBD) interactions of structures and properties in the gas phase and implicit water. Thus, AQM contains over 40 global and local physicochemical properties (including ground-state and response properties) per conformer computed at the tightly converged PBE0+MBD level of theory for gas-phase molecules, whereas PBE0+MBD with the modified Poisson-Boltzmann (MPB) model of water was used for solvated molecules. By addressing both molecule-solvent and dispersion interactions, AQM dataset can serve as a challenging benchmark for state-of-the-art machine learning methods for property modeling and de novo generation of large (solvated) molecules with pharmaceutical and biological relevance.

The alloyed cementite (Fe–Ni–Cr)3C: Local environment, atomic magnetic moments, and magnetization from DFT calculation

The alloying element added to carbon steel to enhance its properties also penetrates Fe3C cementite particles, altering their properties and influencing the steel product through them. This is why the impact of alloying elements on cementite has been extensively studied. Ni and Cr exhibit opposing behavior in cementite, so cementite doped with Ni and Cr is investigated using DFT calculations. The data obtained for total energy, lattice, magnetization, local magnetic moments at metal atoms, and their nearest environment are compared to experimental magnetic data for Ni and Cr-alloyed cementite. The relationship between Fe atom magnetic moments and their nearest environment is discussed in comparison between Cr and Ni doping. Decrease in magnetization with Ni and Cr content is attributed to 1) replacement of a larger Fe magnetic moment (mFe = 1.9–2.0 μB) with a smaller or even negative moment (mNi = 0.2–0.5 μB, mCr = −0.3 to −1.0 μB); 2) a decrease in the average Fe moment with the number of Cr atoms in the nearest environment; and 3) a strong dependence of the Curie temperature on Cr content in Cr-doped cementite.

The Reconstruction of Pt(001) Surface and the Shell-Like Reconstruction of the Vicinal Pt(001) Surfaces Revealed by Neural Network Potential.

In this work, a highly accurate neural network potential (NNP) is presented, named PtNNP, and the exploration of the reconstruction of the Pt(001) surface and its vicinal surfaces with it. Contrary to the most accepted understanding of the Pt(001) surface reconstruction, the study reveals that the main driving force behind Pt(001) quasi-hexagonal reconstruction is not the surface stress relaxation but the increased coordination number of the surface atoms resulting in stronger intralayer binding in the reconstructed surface layer. In agreement with experimental observations, the optimized supercell size of the reconstructed Pt(001) surface contains (5×20) unit cells. Surprisingly, the reconstruction of the vicinal Pt(001) surfaces leads to a smooth shell-like surface layer covering the whole surface and diminishing sharp step edges.

Orbital magnetic susceptibility of zigzag carbon nanobelts: a tight-binding study

The magnetic properties of a circular graphene nanoribbon (carbon belt) in a magnetic field parallel to its central axis is studied using a tight-binding model. Orbital magnetic susceptibility is calculated using an analytical expression of the energy eigenvalues as a function of the magnetic flux density for any size, and its temperature dependence is considered. In the absence of electron hopping parallel to the magnetic field, the orbital magnetic susceptibility diverges at absolute zero if the chemical potential is zero and the number of atoms is a multiple of four. As the temperature increases, the magnitude of susceptibility decreases according to the power law, whose exponent depends on the size. In the presence of electron hopping parallel to the magnetic field, the divergence of the susceptibility near absolute zero disappears, and the sign changes with the transfer integral parallel to the magnetic field and the temperature.

Photoinduced Phase Transitions of Imine-Based Liquid Crystal Dimers with Twist–Bend Nematic Phases

Photoisomerizable molecules in liquid crystals (LCs) allow for photoinduced phase transitions, facilitating applications in a wide variety of photoresponsive materials. In contrast to the widely investigated azobenzene structure, research on the photoinduced phase-transition behavior of imine-based LCs is considerably limited. We herein report the thermal and photoinduced phase-transition behaviors of photoisomerizable imine-based LC dimers with twist–bend nematic (NTB) phases. We synthesize two homologous series of ester- and thioether-linked N-(4-cyanobenzylidene)aniline-based bent-shaped LC dimers with an even number of carbon atoms (n = 2, 4, 6, 8, and 10) in the central alkylene spacers, namely, CBCOOnSBA(CN) and CBOCOnSBA(CN), possessing oppositely directed ester linkages, C=OO and OC=O, respectively. Their thermal phase-transition behavior is examined using polarizing optical microscopy and differential scanning calorimetry. All dimers form a monotropic NTB phase below the temperature of the conventional nematic (N) phase upon cooling. Remarkably, the NTB phases of CBCOOnSBA(CN) (n = 2, 4, 6, and 8) and CBOCOnSBA(CN) (n = 6 and 8) supercool to room temperature and vitrify without crystallization. In addition, the phase-transition temperatures and entropy changes of CBCOOnSBA(CN) are lower than those of CBOCOnSBA(CN) at the same n. Under UV light irradiation, the NTB and N phases transition to the N and isotropic phases, respectively, and reversibly return to their initial LC phases when the UV light is turned off.

Velocity selective multiple two-photon dark and bright resonances in Potassium vapor

We report the observation of two additional sub-natural line width quantum interferences in the D 2 manifold of 39 K vapor, in addition to the usual single Electromagnetically Induced Transparency (EIT) peak. In a typical three level Λ-type system, only one EIT peak is observed. However, here we report observation of two additional line shapes riding on top of the absorption profile. The fact that the hyperfine splitting is smaller than the Doppler width in 39 K allows the probe and control beams to swap their transition pathways in different velocity groups of atoms even when their frequencies are kept constant. Our observations are in striking contrast to standard EIT measurements. These findings are in quantitative agreement with density matrix formalism taking into account velocity-selective two-photon resonances. Owing to the favorably low ground hyperfine splitting (Δ hf ) in 39 K, which allows a significantly large number of atoms with a Doppler shift greater than or equal to the Δ hf , the strength of these additional resonances is strong compared to that of other alkali atoms such as 87 Rb, 133 Cs where these resonances can not be observed. The control photon detuning to atomic transition captures the nature of the coherence; therefore an unusual phenomenon of conversion from perfect transparency to enhanced absorption of the probe photon is observed and explained by utilizing the adiabatic elimination of the excited state in the Master equation. Controlling such dark and bright resonances leads to new applications in quantum technologies such as frequency-offset laser stabilization and long-lived quantum memory.

Odd-Even Alkyl Chain Effects on the Structure and Charge Carrier Transport of Two-Dimensional Sn-Based Perovskite Semiconductors.

Oscillations in the chemical or physical properties of materials, composed of an odd or even number of connected repeating methylene units, are a well-known phenomenon in organic chemistry and materials science. So far, such behavior has not been reported for the important class of materials, perovskite semiconductors. This work reports a distinct odd-even oscillation of the molecular structure and charge carrier transport properties of phenylalkylammonium two-dimensional (2D) Sn-based perovskites in which the alkyl chains in the phenylalkylammonium cations contain varying odd and even carbon numbers. Density functional theory calculations and grazing-incidence wide-angle X-ray scattering characterization reveal that perovskites with organic ligands containing an alkyl chain with an odd number of carbon atoms display a disordered crystal lattice and tilted inorganic octahedra accompanied by reduced mobilities. In contrast, perovskites with cations of an even number of carbon atoms in the alkyl chain form more ordered crystal structures, resulting in improved charge carrier mobilities. Our findings disclose the importance of minor changes in the molecular conformation of organic cations have an effect on morphology, photophysical properties, and charge carrier transport of 2D layered perovskites, showcasing alkyl chain engineering of organic cations to control key properties, of layered perovskite semiconductors.

The alloyed cementite (Fe-Ni-Cr)3C: local environment, atomic magnetic moments, and magnetization from DFT calculation

The alloying element added to carbon steel to enhance its properties also penetrates Fe3C cementite particles, altering their properties and influencing the steel product through them. This is why the impact of alloying elements on cementite has been extensively studied. Ni and Cr exhibit opposing behavior in cementite, so cementite doped with Ni and Cr is investigated using DFT calculations. The data obtained for total energy, lattice, magnetization, local magnetic moments at metal atoms, and their nearest environment are compared to experimental magnetic data for Ni and Cr-alloyed cementite. The relationship between Fe atom magnetic moments and their nearest environment is discussed in comparison between Cr and Ni doping. Decrease in magnetization with Ni and Cr content is attributed to 1) replacement of a larger Fe magnetic moment (mFe=1.9-2.0 μB) with a smaller or even negative moment (mNi=0.2-0.5 μB, mCr=-0.3 – -1.0 μB); 2) a decrease in the average Fe moment with the number of Cr atoms in the nearest environment; and 3) a strong dependence of the Curie temperature on Cr content in Cr-doped cementite.

Controlling dark solitons on the healing length scale

While usually the optical diffraction limit is setting a limit for the lengthscales on which a typical alkali Bose–Einstein condensate can be controlled, we show that in certain situations control via matter waves can achieve smaller resolutions. For this we consider a small number of impurity atoms which are trapped inside the density dip of a dark soliton state and show that any grey soliton state can be obtained by selectively driving the impurity atoms. This allows to fully control the position and velocity of the dark soliton, and also study controlled collisions between these non-linear objects.

Unveiling the Potential of Haloalkenes as Electron Density Acceptors.

We report herein, by means of structural and computational analyses, a comprehensive study of the capability of differently substituted haloalkenes to behave as electron density acceptors in noncovalent interactions. The nature of these interactions between haloalkenes and Lewis bases highly depends on the number and nature of the halogen atoms bound to the carbon-carbon double bond. When hydrogen bonds, which generally dominate for mono- and dihaloalkenes, cannot be formed, we observe the establishment of attractive interactions in which an sp2 carbon atom, belonging to an acyclic C=C double bond, plays the role of the Lewis acid via its π* antibonding orbital.

WITHDRAWN: Molecular dynamics calculations on the Glass temperature and crystallization process of AgAu alloy

In this paper, the molecular dynamics (MD) model is used to study the glass temperature and crystallization process of AgAu alloy under the influence of several factors such as heating rate, atomic number, temperature, annealing time on structural shape, number of structural units, phase transition, and crystallization process. The results show that using the Sutton-Chen (SC) embedded interaction force field and periodic boundary conditions achieved results that are completely consistent with previous results. When increasing the number of atoms and annealing time, the crystallization process increases, and when increasing the heating rate and temperature, the crystallization process decreases. The result of the phase transition is shown when a decrease in temperature leads to increased crystallization and the material changes from a liquid state to a crystalline or amorphous state. The crystallization process is expressed through the number of structural units face-centered cubic (FCC), hexagonal close-packed (HCP), body-centered cubic (BCC), amorphous (Amor), surface shape, radial distribution function (RDF), size (l) and total energy of the system (Etot). When changing the factors that lead to the height of the radial distribution function of the Ag-Au link changing greatly, the length of the Ag-Au link has a very small change in value and is almost constant with rAg-Au = 2.78 Å, when increasing the annealing time, the link length increases to 2.88 Å, and when increasing the heating rate, the link length decreases to 2.68 Å. In addition, successfully determined the glass temperature with AgAu alloy with a 50% Au doping concentration of 535 K. The results obtained with AgAu alloy can be used as a basis for future experimental studies to research and manufacture biosensors for applications in the fields of science, engineering, biology, and medicine.

Spatial calibration of high-density absorption imaging

The accurate determination of atom numbers is an ubiquitous problem in the field of ultracold atoms. For modest atom numbers, absolute calibration techniques are available, however, for large numbers and high densities, the available techniques neglect many-body scattering processes. Here, a spatial calibration technique for time-of-flight absorption images of ultracold atomic clouds is presented. The calibration is obtained from radially averaged absorption images and we provide a practical guide to the calibration process. It is shown that the calibration coefficient scales linearly with optical density and depends on the absorbed photon number for the experimental conditions explored here. This allows for the direct inclusion of a spatially dependent calibration in the image analysis. For typical ultracold atom clouds the spatial calibration technique leads to corrections in the detected atom number up to ≈12% and temperature up to ≈14% in comparison to previous calibration techniques. The technique presented here addresses a major difficulty in absorption imaging of ultracold atomic clouds and prompts further theoretical work to understand the scattering processes in ultracold dense clouds of atoms for accurate atom number calibration.

Descriptors-based machine-learning prediction of cetane number using quantitative structure–property relationship

The physicochemical properties of liquid alternative fuels are important but difficult to measure/predict, especially when complex surrogate fuels are concerned. In the present work, machine learning is used to develop quantitative structure–property relationship models. The fuel chemical structure is represented by molecular descriptors, allowing the linking of important features of the fuel composition and key properties of fuel utilization. Feature selection is employed to select the most relevant features that describe the chemical structure of the fuel and several machine learning algorithms are tested to construct interpretable models. The effectiveness of the methodology is demonstrated through the development of accurate and interpretable predictive models for cetane numbers, with a focus on understanding the link between molecular structure and fuel properties. In this context, matrix-based descriptors and descriptors related to the number of atoms in the molecule are directly linked with the cetane number of hydrocarbons. Furthermore, the results showed that molecular connectivity indices play a role in the cetane number for aromatic molecules. Also, the methodology is extended to predict the cetane number of ester and ether molecules, leveraging the design of alternative fuels towards fully sustainable fuel utilization.

Geometries, electronic structures, mechanical properties and stabilities of Fe128Hen and Fe127VacHen: An uniaxial compression effect

Owning to the factors of external mechanical loads and high heat flux deposition, various degrees of strain or stress are inevitably introduced into the structural materials of nuclear fusion reactors. The uniaxial compression effects on the geometries, electronic structures, mechanical properties, and stabilities of Fe128Hen and Fe127VacHen were studied by first-principles calculations in this work. The results show that the lattice suffers from a noticeable inclination or disorder as the strain reaches 15%. The maximum stress of the stress–strain curves implied that the mechanical characteristics decay considerably as the number of He atoms increases, but the presence of a vacancy mitigated this effect. Compressive strain decreases the stability of Fe atom in the perfect pure Fe system, but it slightly elevates the monovacancy formation energy from Fe128He3 onward. According to the binding energy of He-He, compressive strain enhanced the aggregation of He. The migration barriers of an interstitial He atom exhibit anisotropy under uniaxial compressive strain, which was explained by the variations of the surrounding architectures.

Soft solution state and hard aging state of Inconel 718 reached via optimized precipitation elements using cluster formula approach

The superior high-temperature performance of Inconel 718 is originated mainly from the precipitation strengthening via Nb, Al, and Ti alloying. Inappropriate contents of the precipitation elements may lead to over-strengthened solution state and insufficiently strengthened aging state. We have previously identified the alloy composition formula [(Nb,Al,Ti)1-(Ni,Fe,Cr,Mo)12](Ni,Fe,Cr,Mo)5 using the cluster formula approach, where the 18-atom structural unit is composed of a nearest-neighbor cluster, centered by one precipitation elements, plus five glue atoms situated at the next neighbors. On the basis of this formula, the present work designs a series of alloys using (Nb,Al,Ti) = 0.93, 1, and 1.06, with 4.9 and 5.5 wt % Nb, 0.68 and 0.5 wt % Al, and 1.10 wt% Ti corresponding to the upper-to-middle ranges in the ASTM standard. In particular, when the total number of atoms in the formula is equal to one, (Nb0.6Al0.2Ti0.2), the alloy is soft at the solution state (σUTS = 825 MPa < 965 MPa of the standard and EL = 70.3 % > 30 %) and reaches high strength levels after aging (σUTS = 1400 MPa > 1240 MPa and EL = 23.4 % > 12 % at room temperature, σUTS = 1100 MPa > 965 MPa and EL = 10.2 % > 5 % at 923 K). This alloy also shows the lowest coarsening rate of 4–7 × 10−3 nm3 s−1 after long-term aging at 923 K, lower than the prevailing coarsening rate of about 16 × 10−3 nm3 s−1.

Crystal chemistry and ionic conductivity of garnet-type solid-state electrolyte, Li5-xLa3(NbTa)O12-y

Crystal structures, microtopography, morphologies, elemental compositions, and ionic conductivity have been investigated for Li5-xLa3(Nb,Ta)O12-y using X-ray diffraction (XRD), field-emission analytical scanning and transmission electron microscopies (S/TEM), and electrochemical impedance spectroscopy. Using Rietveld refinements with powder XRD patterns, we determined that the number of Li atoms in the formula is less than 5 and that Li5-xLa3(NbTa)O12-y crystallizes in the cubic garnet structure with a space group Ia-3d. Sintering at varying temperatures (750–1000 °C) for 5 h in an ambient atmosphere produced distinct outcomes. Rietveld refinements disclosed that the sample sintered at 1000 °C (Li3.43(2)La3Nb1.07(2)Ta0.93(2)O12-y, a = 12.8361(7) Å, V = 2114.96(3) Å3) exhibited the highest ionic conductivity, while the 850 °C sample had the lowest conductivity, characterized by lower Li concentration and impurity phases (Li(Nb,Ta)3O88, Li2CO3). Analyses, including XRD and electron microscopy, confirmed the 1000 °C sample as a relatively phase pure with enhanced Li content (Li/La = 1.2), larger grains (15 μm), and uniform crystallinity. The 1000 °C sample introduced additional partially filled Li3 (96h) sites, promoting Li migration, and enhancing ionic conductivity. The resulting XRD pattern at 1000 °C has been submitted to the Powder Diffraction File as a reference.