Atomic Core Research Articles

The Effects of Chemical Bonding at Subatomic Resolution: A Case Study on α-Boron.

Similar to classical asphericity shifts, aspherical deformations of the electron density in the atomic core region can result in core asphericity shifts in refinements using a Hansen-Coppens multipolar model (HCM), especially when highly precise experimental datasets with resolutions far beyond sin(θ)/λ ≤ 1.0 Å−1 are employed. These shifts are about two orders of magnitude smaller than their counterparts caused by valence shell deformations, and their underlying deformations are mainly of dipolar character for 1st row atoms. Here, we analyze the resolution dependence of core asphericity shifts in α-boron. Based on theoretical structure factors, an appropriate Extended HCM (EHCM) is developed, which is tested against experimental high-resolution (sin(θ)/λ ≤ 1.6 Å−1) single-crystal diffraction data. Bond length deviations due to core asphericity shifts of α-boron in the order of 4–6·10−4 Å are small but significant at this resolution and can be effectively compensated by an EHCM, although the correlation of the additional model parameters with positional parameters prevented a free refinement of all core model parameters. For high quality, high resolution data, a proper treatment with an EHCM or other equivalent methods is therefore highly recommended.

Forbidden transitions between the 2p3/2 and 2p1/2 states of ground B-like ions with 14 ≤ Z ≤ 92

The magnetic-dipole M1 and electric quadrupole E2 transition energies and rates between the two fine structure states of 1s22s22p configuration for B-like ions with 14 92 have been calculated using the multi-configuration Dirac-Fock (MCDF) method. The interactions with atomic core have been considered and the core-valence correlation contributions to the level energies are evaluated in the active space approximation. The finite nuclear size, the frequency dependent and independent Breit interaction and quantum electrodynamics (QED) corrections have been included in the calculations. To improve the accuracy of the present data on the forbidden line energies and rates, the QED corrections to the transition energies have been adjusted using QEDMOD code with MCDF wavefunctions. The sensitivity of the transition parameters on the nature of the spin orbitals has been probed by considering two sets of calculations, one with fully relaxed and the other with a common set of radial functions. The present line energies and lifetime of the 2s22p 2 p 3/2 state are found to be in excellent agreement with available experimental and theoretical data.

New insight into the mechanism of carbon dioxide activation on copper-based catalysts: A theoretical study

A combination of Artificial Bee Colony algorithm, eXtended Tight Binding and Density functional theory methods were performed to study the activation process of carbon dioxide (CO2) over copper (Cu4 cluster) based catalytic systems. The findings revealed that the activation of the C–O bond resulted from the electron transfer to σ*, π* - MO of CO2. The more the electrons are transferred to CO2, the more the C–O bond is activated and elongated. The suitability of several metal oxide supports (Fe2O3, Al2O3, MgO, ZnO) is estimated using calculated electronic parameters (global electrophilicity index, vertical ionization potential and vertical electron affinity). Aside from demonstrating the appropriateness of Al2O3 and ZnO, a thorough examination of MgO revealed that, due to the formation of stable carbonate products, this oxide is not really appropriate as a support for copper-based catalysts in CO2 conversion. Our studies have also shown that the electron enrichment of copper atoms plays a key role in the activation of C–O bonds. Alkali metal doping (Li, K, Cs) significantly improves the catalytic efficiency of the Cu4 cluster. Based on the results of electron transfer to the CO2 molecule, the effect of doping alkali metal atoms may be organized in the following order: Cs > K > Li. A new core/shell catalytic system with potassium atoms in the core and copper atoms in the shell has been proposed and has proven to be a promising, efficient catalytic system in the CO2 adsorption and activation.

Influence of dissipation and effective interaction on the dense plasma dynamic structure factor.

The ionic dynamic structure factor is examined to assess the relative roles of dissipation and the effective ionic interaction. Two disparate physically based models of dissipation, which can differ numerically by orders of magnitude, are used in molecular dynamics. We find a negligible impact on the amplitudes of the dynamic structure factors for physically realistic parameter values. We then examine the effective ionic interaction by varying its strength, the size of the atomic core (through a pseudopotential), and the screening model. We find that "diffusive" peaks in the dynamic structure factor are very sensitive to the form of the ionic interaction, and this sensitivity arises primarily from atomic physics through the pseudopotential. This suggests that it would be useful to employ the measured zero-frequency dynamic structure factor S_{ii}(k,0) as a constraint on the effective interaction, which in turn can be used to compute physical properties.

Theoretical study on dry reforming of methane catalyzed by Cu12M (M = Cu, Fe, Co, Ni) core-shell bimetallic clusters

Dry reforming of methane (DRM) reaction can not only effectively solve the greenhouse effect, but also produce H2 and CO, which are important raw materials and intermediates for Fischer-Tropsch synthesis. In this paper, the mechanism of DRM on Cu12M (M = Cu, Fe, Co, Ni) core-shell bimetallic nanoclusters was studied by density functional theory (DFT). The Mulliken charge distribution indicates that the charge in the core-shell structure is transferred to the shell atom (Fe, Co, Ni) through the core atom (Cu). The results of binding energy and bond length indicate that Fe, Co and Ni as core atoms enhance the structural stability of Cu13 nanoclusters. The analysis of partial density of states (PDOS) and d-band center indicates that Cu12Ni is the most potential DRM catalyst due to the highest electronic activity. The mechanism study shows that Cu13, Cu12Co and Cu12Ni all react in the same path, while Cu12Fe takes another route. The rate-determining step is CH3* → CH2* + H*, and the total energy barrier of DRM on Cu12Ni nanocluster is relatively the lowest, which is the most cluster to catalytic DRM reaction.

Solvated electrons in the complex media: a review

<p indent="0mm">Solvated electrons are a type of weakly-bound electrons which are confined in solvents or surrounding media and are different from the atomic core and valence electrons. Their main characters are that the electron(s) are solvated by solvent molecules or micro-surrounding media, and are novel entities and special quantum dot systems. They have quite unique structures, properties and dynamics, and exhibit the promising applications. In this review, we summarized the serial research progress about the solvated electrons in the complex media by our group, including the structures, states, properties, time-evolution dynamics of their character parameters in the complicated media, a series of chemical reactions and physical process associated with solvated electrons, and functionality of solvated electron systems, discussed their characteristics and regularities, and also presented the outlook for the further development of the solvated electrons.<bold> </bold>

Photoionization of nS and nD Rydberg atoms of Rb and Cs from the near-infrared to the ultraviolet spectral region

We present calculations of the photoionization (PI) cross sections of rubidium and cesium Rydberg atoms for light with wavelengths ranging from the infrared to the ultraviolet, using model potentials from Marinescu et al (1994 Phys. Rev. A 49 982). The origins of pronounced PI minima are identified by investigating the free-electron wavefunctions. These include broad PI minima in the nS to ϵP PI channels of both Rb and Cs, with free-electron energy ϵ, which are identified as Cooper minima. Much narrower PI minima in the nD to ϵF channels are due to shape resonances of the free-electron states. We describe possible experimental procedures for measuring the PI minima, and we discuss their implications in fundamental atomic physics as well as in practical applications. Measurements of PI cross sections of Rydberg atoms may serve as a sensitive probe for many-electron interactions of the Rydberg electron in the atomic core region.

The chemistry of spin-coated rhodium-ferrocenyl complexes supported on silanol-capped silicon wafers

A series of rhodium β-diketonato complexes [Rh(FcCOCHCOR)(CO)2] and [Rh(FcCOCHCOR)(CO)(PPh3)] with R = CF3, CH3, Ph = C6H5 and Fc (ferrocenyl = FeII(C5H5)(C5H4)) were spin-coated on two-dimensional silanol-functionalised silicon wafers. Chemical reactions were observed that do not occur in ethanol solutions. Si-OH fragments on the wafers substituted ligands and oxidatively added to the Rh(I) centres. A multitude of different surface species could be identified with X-ray photoelectron spectroscopy (XPS). These included the parent spin-coated rhodium(I) complexes and rhodium(I) species that resulted from β-diketonato displacement from parent rhodium complexes by surface silanol OH’s to generate [wafer-(O)2-Rh-(CO)2]⊝ and [wafer-(O)2-Rh-(CO)(PPh3)]⊝ units. Several RhIII surface species that inter alia resulted from oxidative addition of surface Si-OH groups to surface-coordinated RhI core atoms were also identified. Efficacy of β-diketonato ligand substitution by the silanol surfaces is a kinetically driven process and can be related to the rate of solution-phase β-diketonato substitution by 1,10-phenanthroline from parent [Rh(FcCOCHCOR)(CO)2] and [Rh(FcCOCHCOR)(CO)(PPh3)] complexes. The binding energies of the RhI and RhIII 3d5/2 photoelectron lines were found to be functions of Gordy scale R-group electronegativities and they are also linearly related to electrochemically determined RhI oxidation potentials.

Truly Monodisperse Molecular Nanoparticles of Cerium Dioxide of 2.4 nm dimensions: A {Ce100 O167 } Cluster.

Ultra-small nanoparticles of CeO2 obtained in molecular form, so-called molecular nanoparticles, have been limited to date to a family whose largest member is of nuclearity Ce40 with a {Ce40 O58 } core atom count. Herein we report that a synthetic procedure has been developed to the cation [Ce100 O149 (OH)18 (O2 CPh)60 (PhCO2 H)12 (H2 O)20 ]16+ , a member with a much higher Ce100 nuclearity and a {Ce100 O167 } core that is more akin to the smallest ceria nanoparticles. Its crystal structure reveals it to possess a 2.4 nm size and high D2d symmetry, and it has also allowed identification of core surface features including facet composition, the presence and location of Ce3+ and H+ (i.e. HO- ) ions, and the binding modes of the ligand monolayer of benzoate, benzoic acid, and water ligands.

Truly Monodisperse Molecular Nanoparticles of Cerium Dioxide of 2.4 nm dimensions: A {Ce100O167} Cluster

AbstractUltra‐small nanoparticles of CeO2 obtained in molecular form, so‐called molecular nanoparticles, have been limited to date to a family whose largest member is of nuclearity Ce40 with a {Ce40O58} core atom count. Herein we report that a synthetic procedure has been developed to the cation [Ce100O149(OH)18(O2CPh)60(PhCO2H)12(H2O)20]16+, a member with a much higher Ce100 nuclearity and a {Ce100O167} core that is more akin to the smallest ceria nanoparticles. Its crystal structure reveals it to possess a 2.4 nm size and high D2d symmetry, and it has also allowed identification of core surface features including facet composition, the presence and location of Ce3+and H+ (i.e. HO−) ions, and the binding modes of the ligand monolayer of benzoate, benzoic acid, and water ligands.

Double photoionization of atomic oxygen: Feshbach resonances in the two-electron continuum

We describe a joint experimental and theoretical investigation on oxygen double photoionization—the emission of two electrons from atomic oxygen following single photon absorption. High-resolution experimental measurements were performed at the Advanced Light Source, revealing sharp resonance structure superimposed on the more familiar Wannier-like, nearly-linear background. These resonance features are attributed to ionization-plus-excitation Feshbach resonances embedded in the double ionization continuum, doubly-excited states that lie above the double-ionization threshold. Such features are absent in the double photoionization cross section of He, or other quasi-two-electron systems, for which the doubly-ionized atomic core remains inert. For a corresponding theoretical analysis, the R-matrix with pseudostates (RMPS) method was invoked by calculating final-state, two-electron resonances-plus-continua wavefunctions and corresponding single-photon absorption cross sections. Overall agreement is found in the direct, background double photoionization cross section. However, the RMPS method, using a small basis due to practical computational limitations, was unable to reproduce quantitatively the smooth background or the sharper resonance features observed in the measurements, showing instead large-scale oscillations about the experimental background, and characteristic pseudoresonance jitter, associated with an insufficient convergence of the pseudostate representation to the true two-electron infinite series of Feshbach resonances embedded in the two-electron continuum. The prominent resonance structure observed highlights the need to consider multiple excitation processes in atoms more complex than He or quasi-two-electron systems.

Chaotic evolution of the energy of the electron orbital and the hopping integral in diatomic molecule cations subjected to harmonic excitation

We analysed the dynamics of the positively charged ions of diatomic molecules (X2+ and XY+), in which the bond is realized by the single electron. We assumed that the atomic cores separated by the distance R were subjected to the external excitation of the harmonic type with the amplitude A and frequency Ω. We found the ground states of ions using the variational approach within the formalism of second quantization (the Wannier function was reproduced by means of Gaussian orbitals). It occurred that, on the account of the highly non-linear dependence of the total energy on R, the chaotic dynamics of cores induced the chaotic evolution of the electronic Hamiltonian parameters (i.e. the energy of the electron orbital ε and the hopping integral t). Changes in cation masses or in the charge arrangement does not affect qualitatively the values of Lyapunov exponents in the A-Ω parameter space.

PENERAPAN MODEL PEMBELAJARAN STAD DENGAN MENGGUNAKAN MEDIA PEMBELAJARAN DALAM MENINGKATKAN HASIL BELAJAR FISIKA SISWA KELAS XII MIPA 8 SMA NEGERI 7 DENPASAR TAHUN PELAJARAN 2020/2021

The purpose of this study was to determine whether there was a student response and the effect of the application of the STAD learning model in improving the physics learning achievement of students in class XII MIPA 8 SMA Negeri 7 Denpasar in the academic year 2020/2021 in the Atomic Core material. This type of research is a classroom action research (PTK). Action research was carried out by means of online virtual zoom animals. In this study, the STAD (Student Team Achievement Division) type cooperative learning model was used. The study used a qualitative descriptive design with two cycles of cooperative learning model type STAD including planning, implementing, observing / evaluating and reflecting. The subjects of this study were 36 students of class XII MIPA 8 at SMA Negeri 7 Denpasar with a total of 36 students. This research was conducted at SMA Negeri 7 Denpasar. It can be concluded as follows: (1) There is an effect of the application of the STAD learning model in improving students' physics learning achievement. (2) There is a student response to physics lessons on the application of the STAD Type Cooperative learning model in improving students' physics learning achievement is good. The increase in the average value is 13.47%. The average processing of student observations from the first cycle an average of 71.55 and the average of the second cycle increased to 81.20.

Icosahedral clusters in Cu100-xZrx (x=32,34,36,38.2,40 at.%) metallic glasses near the peak of glass-forming ability (x=36): A balance between population and encaging strength

Understanding the origin of glass-forming ability (GFA) is important for the discovery or development of new metallic glasses (MGs). It is well known that the GFA in Cu–Zr binary MGs is sensitive to the composition and possesses a peak around Cu64Zr36 (at.%). The reason for this, however, is still not fully understood due to the complexity of the physics behind glass formation. Here, we use molecular dynamics simulations and statistics to study the structure and particularly the atomic energy state of the supercooled liquid and glass phases in the Cu100-xZrx (x = 32, 34, 36, 38.2, 40 at.%) alloy series. We show that the shell atoms of icosahedral clusters (the most dominant cluster type) in all these alloys have significantly lower (by > 1 eV/atom) potential energy than the core atoms. With rising Zr-content, the core–shell energy difference of the icosahedral clusters increases, making these clusters more strongly encaged and harder to break before or during crystallization. This effect counteracts the decrease in the population of the icosahedral clusters that has been noticed in previous studies. The net result of the interplay between these two factors can be represented by the product of the fraction of icosahedral shell-atoms and the core-shell energy difference, which exhibits a maximum at 36% Zr where the highest GFA has been observed. These findings provide new insights into the origin and peaking behavior of the GFA in this important binary bulk MG system, which could facilitate the search for the best glass-forming compositions in other alloy systems.

Magnetic Properties of Mn2RhSi Heusler Alloy: Phase Transition and Hysteresis Behavior at a Very Low Temperature

Using Kaneyoshi approximation in the framework of effective field theory, we have carried out theoretically the magnetic phase transition and hysteresis behavior at a very low temperature in Mn2RhSi Heusler Alloy (Mn2RhSi-HA). The alloy shows to a ferrimagnetic successive phase transition while its atoms exhibit a various successive phase transition with Tt = 0.630 and TC = 1.560. At a very low temperature, we attain that the alloy has a multistep hysteresis behavior having a butterfly-like hysteresis loop with a large coercivity field while the Si1 atom shows a type-II superconducting hysteresis behavior. Step-like hysteresis behavior at low temperature is due to quantum tunneling of the magnetization. So, we suggest Mn2RhSi-HA could be a potential candidate for magnetic storage device application. Moreover, we can conclude that the competition of antiferromagnetic and ferromagnetic exchange couplings leads to the variety of magnetic phase transition and the hysteresis behavior in Mn2RhSi-HA and its atoms. We can also conclude that these atoms and their exchange interactions to other atoms make a significant contribution to controlling the hysteresis behavior of Mn2RhSi-HA, since the Mn and Rh2 core atoms have the same coercivity as that of Mn2RhSi-HA. The obtained results are consistent with the reported experimental and theoretical results of Mn2-based Heusler alloys and other alloys.

Simulation of Electronic Structure and some Properties of CdTe Crystals Using DFT

The current study investigated the electrical properties of Cadmium Telluride (CdTe)by using the first principle of density functional theory (DFT). The nanocrystals suggested being varied constantly over the network systematically so that the lowest value for energy is obtained, through which stability is obtained and through this exceptionality, the measurements of the properties are in their exact state. The conduction and the valence bandwidths were also studied. The investigations targeted the “highest occupied molecular orbital” (HOMO) [Ionization Potential], and the “lowest unoccupied molecular orbital” (LUMO) [Electron Affinity]. Total and cohesive energies, the atomic iconicity, electron affinity, energy gap (Eg), and the density of states (DOS) for 8, 16, 54, and 64 atoms. The results showed that the shape of the conduction and valence affect the crystal groups significantly, and the energy gap exhibited very close results to their practical counterparts that were previously conducted. When the lattice constant decreases the modulus of bulk and the waves of sound speed increase with the increase of the core atoms number. Subsequently, the applied pressure increases the Plasmon energy and bulk modulus. The key of study is to inspect if using materials in their nanoscale state gives special physical, electronic and optical properties through which devices are manufactured with high efficiency in the solar cell industry. Where the compound becomes a point of a sleeve, and the fluorescent peak shifts across the visible field to the UV field. This was obtained by controlling the size of the compound in 54 and 64, at which the energy gap showed an increase, which would make it more preferred to stimulate the electron from the valence band to the conduction band.

Studies of Ultrafast Molecular Dynamics by Femtosecond Extreme Ultraviolet Absorption Spectroscopy

Transient absorption spectroscopy is one of the most widely used experimental techniques for time-resolved studies of ultrafast phenomena. Recent advances in the generation of short-wavelength pulses of ultrashort duration have made transient absorption probing of atomic core level transitions possible. In this Highlight Review, we introduce our recent work on using extreme ultraviolet (XUV) transient absorption spectroscopy to investigate the ultrafast molecular dynamics induced by intense laser fields. While investigations of intense laser-molecule interaction have primarily focused on elucidating electron dynamics, it is important to understand the vibrational dynamics that are triggered by intense laser fields because of their coupling to electron dynamics. Probing the iodine 4d core level, our XUV transient absorption studies of iodoalkanes irradiated by intense laser fields elucidate ultrafast dissociative ionization dynamics and vibrational wave packet dynamics. Time-dependent XUV spectral shifts and global analysis of time-resolved XUV transient absorption spectra can be used to reconstruct C–I dissociation dynamics and identify multiple dissociation channels. In addition, XUV transient absorption spectroscopy also unravels both small- and large-amplitude coherent vibrational motion, whose origin can be identified by analyzing the phase of the oscillatory XUV transition energies. Our studies show that XUV transient absorption spectroscopy is a powerful technique for the study of ultrafast molecular dynamics.

Metallic line defect in wide-bandgap transparent perovskite BaSnO3.

A line defect with metallic characteristics has been found in optically transparent BaSnO3 perovskite thin films. The distinct atomic structure of the defect core, composed of Sn and O atoms, was visualized by atomic-resolution scanning transmission electron microscopy (STEM). When doped with La, dopants that replace Ba atoms preferentially segregate to specific crystallographic sites adjacent to the line defect. The electronic structure of the line defect probed in STEM with electron energy-loss spectroscopy was supported by ab initio theory, which indicates the presence of Fermi level-crossing electronic bands that originate from defect core atoms. These metallic line defects also act as electron sinks attracting additional negative charges in these wide-bandgap BaSnO3 films.

DART: deep learning enabled topological interaction model for energy prediction of metal clusters and its application in identifying unique low energy isomers.

Recently, machine learning (ML) has proven to yield fast and accurate predictions of chemical properties to accelerate the discovery of novel molecules and materials. The majority of the work is on organic molecules, and much more work needs to be done for inorganic molecules, especially clusters. In the present work, we introduce a simple topological atomic descriptor called TAD, which encodes chemical environment information of each atom in the cluster. TAD is a simple and interpretable descriptor where each value represents the atom count in three shells. We also introduce the DART deep learning enabled topological interaction model, which uses TAD as a feature vector to predict energies of metal clusters, in our case gallium clusters with sizes ranging from 31 to 70 atoms. The DART model is designed based on the principle that the energy is a function of atomic interactions and allows us to model these complex atomic interactions to predict the energy. We further introduce a new dataset called GNC_31-70, which comprises structures and DFT optimized energies of gallium clusters with sizes ranging from 31 to 70 atoms. We show how DART can be used to accelerate the process of identification of low energy structures without geometry optimization. Albeit using a topological descriptor, DART achieves a mean absolute error (MAE) of 3.59 kcal mol-1 (0.15 eV) on the test set. We also show that our model can distinguish core and surface atoms in the Ga-70 cluster, which the model has never encountered earlier. Finally, we demonstrate the transferability of the DART model by predicting energies for about 6k unseen configurations picked up from molecular dynamics (MD) data for three cluster sizes (46, 57, and 60) within seconds. The DART model was able to reduce the load on DFT optimizations while identifying unique low energy structures from MD data.

Bimetallic Au-Pd nanoparticles supported on silica with a tunable core@shell structure: enhanced catalytic activity of Pd(core)-Au(shell) over Au(core)-Pd(shell).

A facile ligand-assisted approach of synthesizing bimetallic Au–Pd nanoparticles supported on silica with a tunable core@shell structure is presented. Maneuvering the addition sequence of metal salts, both Aucore–Pdshell (Au@Pd–SiO2) and Pdcore–Aushell (Pd@Au–SiO2) nanoparticles were synthesized. The structures and compositions of the core–shell materials were confirmed by probe-corrected HRTEM, TEM-EDX mapping, EDS line scanning, XPS, PXRD, BET, FE-SEM-EDX and ICP analysis. The synergistic potentials of the core–shell materials were evaluated for two important reactions viz. hydrogenation of nitroarenes to anilines and hydration of nitriles to amides. In fact, in both the reactions, the Au–Pd materials exhibited superior performance over monometallic Au or Pd counterparts. Notably, among the two bimetallic materials, the one with Pdcore–Aushell structure displayed superior activity over the Aucore–Pdshell structure which could be attributed to the higher stability and uniform Au–Pd bimetallic interfaces in the former compared to the latter. Apart from enhanced synergism, high chemoselectivity in hydrogenation, wide functional group tolerance, high recyclability, etc. are other advantages of our system. A kinetic study has also been performed for the nitrile hydration reaction which demonstrates first order kinetics. Evaluation of rate constants along with a brief investigation on the Hammett parameters has also been presented.