Atom Chemistry Research Articles

Chemistry and Local Environment Adaptive Representation graphs as material descriptors

Accelerating materials design and property prediction via supervised learning involves manually generating feature vectors or performing complicated atom coordinates transformation, which restricts the model to a limited set of crystal structures or makes it challenging to provide chemical insights. In this work, we devised a unique low-dimensional featurization technique known as "Chemistry and Local Environment Adaptive Representation" (CLEAR) graphs to automatically learn the properties of materials through the chemistry of the atom connections. CLEAR is an adaptive featurization method that integrates the chemistry of atoms with their atomic environment using Voronoi nearest neighbours (NN). In addition, integrating the CLEAR descriptors with explainable machine learning models unravels its potential to obtain numerous scientific insights. We applied this approach to study the stability of compositional and configurational diverse high entropy alloys (HEAs). The proposed framework provides a universal low-dimensional representation with chemistry-informed local environment descriptors, which outperforms the prediction of phases and formation energies in HEAs.

Effect of Extreme Variations of Fundamental Constants on the Structure of Atoms and Molecules.

The fundamental constants (FCs) of physics are promoted to dynamic quantities in modern theories. So far most of the literature focused on small fractional variations in the values of FCs. In this paper, we investigate the novel regime of extreme but transient variations of FCs. We focus on the speed of light (c) and show that its variation can dramatically change the electronic structure and chemistry of atoms and molecules. These changes are induced by increased relativistic effects when c is reduced from its nominal value. To model these changes, we solve the fully relativistic Dirac equation at different values of c. We show that at extreme variations of c, the periodic table is truncated, the nominal ground states of atoms can change, water fails to serve as a universal solvent, and the ammonia molecule becomes planar.

Advances in Atomic Time Scale Imaging with a Fine Intrinsic Spatial Resolution

Atomic time scale imaging, opening a new era for studying dynamics in microcosmos, is presently attracting immense research interest on the global level due to its powerful ability. On the atom level, physics, chemistry, and biology are identical for researching atom motion and atomic state change. The light possesses twoness, the information carrier and the research resource. The most fundamental principle of this imaging is that light records the event-modulated light field by itself, so-called all-optical imaging. This paper can answer what is the essential standard to develop and evaluate atomic time scale imaging, what is the optimal imaging system, and what are the typical techniques to implement this imaging, up to now. At present, the best record in the experiment, made by multistage optical parametric amplification (MOPA), is realizing 50-fs resolved optical imaging with a spatial resolution of ~83 lp/mm at an effective framing rate of 15 × 10 12 fps for recording an ultrafast optical lattice with its rotating speed up to 13.5 × 10 12 rad/s.

Design and Investigation of Superatoms for Redox Applications: First-Principles Studies.

A superatom is a cluster of atoms that acts like a single atom. Two main groups of superatoms are superalkalis and superhalogens, which mimic the chemistry of alkali and halogen atoms, respectively. The ionization energies of superalkalis are smaller than those of alkalis (<3.89 eV for cesium atom), and the electron affinities of superhalogens are larger than that of halogens (>3.61 eV for chlorine atom). Exploring new superalkali/superhalogen aims to provide reliable data and predictions of the use of such compounds as redox agents in the reduction/oxidation of counterpart systems, as well as the role they can play more generally in materials science. The low ionization energies of superalkalis make them candidates for catalysts for CO2 conversion into renewable fuels and value-added chemicals. The large electron affinity of superhalogens makes them strong oxidizing agents for bonding and removing toxic molecules from the environment. By using the superatoms as building blocks of cluster-assembled materials, we can achieve the functional features of atom-based materials (like conductivity or catalytic potential) while having more flexibility to achieve higher performance. This feature paper covers the issues of designing such compounds and demonstrates how modifications of the superatoms (superhalogens and superalkalis) allow for the tuning of the electronic structure and might be used to create unique functional materials. The designed superatoms can form stable perovskites for solar cells, electrolytes for Li-ion batteries of electric vehicles, superatomic solids, and semiconducting materials. The designed superatoms and their redox potential evaluation could help experimentalists create new materials for use in fields such as energy storage and climate change.

O-19 - Auger electrons in radionuclide therapy: Szilárd-Chalmers effect/hot atom chemistry during the targeted delivery of the isotopes

O-19 - Auger electrons in radionuclide therapy: Szilárd-Chalmers effect/hot atom chemistry during the targeted delivery of the isotopes

Pore Diameter and Chemistry Modulated Flexible Ion Selectivity through a Single-Layer MoS2 Nanopore

Nanoporous membranes based on 2D materials are promising as the most efficient technologies for practical engineering applications such as seawater desalination, ion sieving, and gas separation. In this work, we utilize various nanopores in molybdenum disulfide (MoS2) membranes to enable flexible ion selectivity that is tuned efficiently by adjusting pore diameter and surface chemistry. We theoretically uncover the molecular mechanisms that lead to MoS2 nanopores with varied diameters and pore atom chemistry exhibiting distinctly different ion selectivity. MoS2 nanopores with S atoms at the nanopore boundary facilitate K+ ion translocation and rejection of Cl– ions. MoS2 nanopores with Mo atoms at the nanopore boundary permit Cl– ion translocation and reject K+ ions. The average flow velocity of K+ ions in the MoS2 nanopore with S atoms at the nanopore boundary is larger than that of Cl– ions in the MoS2 nanopore with Mo atoms at the nanopore boundary. This phenomenon is attributed to the totally different ion transport mechanisms modulated by the nanopore boundary atoms. This work provides new insights into designing multifunctional membranes on a single 2D material membrane with flexible and optimal ion selectivity toward broad applications.

Water mediated pot, atom, and step economic (PASE) synthesis of pyrimido[4,5-d]pyrimidines using ultrasound and microwave irradiation approaches

The functioning, Pot, Atom, and Step Economic (PASE) green chemistry proposition has been approached for the synthesis of pyrimido[4,5-d]pyrimidines by the multicomponent reaction (MCR) of barbituric acid, guanidine, and aldehyde derivatives using water solvent and iodine catalyst through ultrasound and microwave irradiation methods. Reaction optimization was performed by varying solvents, reaction time, the concentration of catalyst, and reaction methods. Microwave irradiation approach using water solvent and iodine catalyst (8 mol%) with 5 min led to offer the highest yield. EWG substituted compound 4 g (4-NO2, guanidine) [87% (U.S.), 93% (M.W.)] was found to be the highest yielded compound in this study. The greenness of the reaction was estimated by calculating some green chemistry metrics. The metrics approved the proposed protocol as an ideal, green, and sustainable approach.

Inorganometallic allenes [(Mn(η5-C5H5)(CO)2)2(μ-E)] (E = Si-Pb): bis-allylic anionic delocalisation similar to organometallic allene but differential σ-donation and π-backdonation.

The chemistry of heavy group-14 tetrel atoms is known to diverge from that of the lighter congener carbon. Here, we report the structure and bonding in inorganometallic allenes [(MnCp(CO)2)2(μ-E)] (2E, E = Si-Pb; Cp = η5-C5H5). These inorganometallic allenes are structurally similar to the lighter organometallic analog [(MnCp(CO)2)2(μ-C)] (2C). The bonding analysis of these compounds at the M06/def2-TZVPP//BP86/def2-SVP level of theory identifies a linear Mn-E-Mn spine with delocalised, mutually orthogonal π-systems across this back-bone. This results in a bis-allylic anionic bonding scenario. However, the strength of the Mn-E bonding is found to be weaker in these inorganometallic allenes. The energy decomposition analysis at the BP86/TZ2P//BP86/def2-SVP level of theory further reveals that the bonding in these compounds cannot be represented by one unique heuristic bonding model, but multiple bonding models. For all 2E (E = C-Pb), the Dewar-Chatt-Duncanson bonding model is one of the best bonding representations, where the central tetrel atom acts as a 4e- σ-donor and 4e- π-acceptor. The bonding analysis indicates that the carbon atom in the organometallic allene acts as a better π-acceptor than σ-donor, while the heavier tetrel atoms in the inorganometallic allenes are better σ-donors than π-acceptors. The npz-orbital is found to be a better σ-donor than the valence ns-orbital. However, when the bonding representation is changed to a traditional electron-sharing model, the contribution from the ns-orbital was found to be the largest in comparison to the interaction from the remaining three valence np-orbitals. It can be suggested that the ns-orbitals contribute more towards chemical bonding when participating via an electron-sharing interaction than a donor-acceptor interaction.

Focus on the cold and ultracold chemistry of atoms, ions and molecules

Focus on the cold and ultracold chemistry of atoms, ions and molecules

Electrical Manipulation of Oxygen Ion Migrations for the Voltage‐Controlled Adjustment of Magnetic Anisotropy and Optimized Skyrmion Generations

AbstractWith the prospect of energy‐efficient spintronics by voltage‐controlled magnetic anisotropy (VCMA), various mechanisms are investigated involving electron orbital state modulations for enhanced spin–orbit interactions, couplings with piezoelectric strain, and electrochemical effect at the interface within diverse magnetoelectric coupled material systems. In the present work, chemistry and spatial distributions of atoms are fine‐tuned at the interface between ferromagnetic Co and partially oxidized Gd layers via voltage‐controlled ion migrations, achieving highly sensitive and stable VCMA operations. With combined actions of chemical diffusion and electrical driving of oxygen through amorphous Gd layer, asymmetric electrical adjustments of magnetic anisotropy could be established. Accompanied changes in the domain morphologies in the magnetic thin film layers could also be confirmed at room temperature. As the fine‐adjustments of domain morphology are essential for the skyrmions generation, voltage‐controlled interfacial chemistry and magnetic anisotropy provide an effective route to stable skyrmion generations and manipulations in the low‐power spintronics technology.

Hot atom chemistry: Oxygen at stepped platinum surfaces

It is a paradigm in chemistry that chemical reactions are mainly governed by thermodynamics. Within this assumption, reaction rates can be derived from transition state theory which requires a quasi-equilibrium between reactants and activated transition state complexes that is achieved through friction. However, to reach thermal equilibrium through friction takes some time. Here we show, based on ab initio molecular dynamics simulations of the interaction of molecular oxygen with stepped Pt surfaces, that chemical reactions in heterogeneous catalysis can occur in a non-equilibrium fashion when the excess kinetic energy upon entering the potential well of a reaction intermediate is large enough.

Nanoscale chemistry and ion segregation in zirconia-based ceramic at grain boundaries by atom probe tomography

In this work nanoscale features that are of importance in the stability of yttria-stabilized tetragonal zirconia (Y-TZP) are quantified through atom probe tomography. In-depth analysis of grain boundary chemistry revealed preferential segregation of lighter and smaller ions towards specific grain boundaries. The relationship between elemental segregation and the local atomistic structure is investigated at the sub-nanometer level to gain insights on nanoscale features associated with the tetragonal-monoclinic phase transformation in Y-TZP through grain boundary characterization. Principal component analysis was implemented to reveal any potential biases from varied field evaporation across stabilizer-rich grain boundaries. The observed variations in ion density across different grains suggested a variation in field which was attributed to potential variations in grain crystal orientation. In order to reveal the subtle depletion of oxygen atoms within grain boundaries a new methodology to map oxygen vacancies is proposed, utilizing the relative neighborhood chemistry of individual yttrium atoms.

Misconceptions about the chemistry of aqueous chlorine atoms and HClOH˙(aq), and a revised mechanism for the photochemical peroxydisulfate/chloride reaction.

It is widely considered that aqueous chlorine atoms (Cl˙) convert to the species HClOH˙ with a half life of about 3 μs and that this species plays an important role in the chemistry of aqueous chlorine atoms. Here it is shown that there is no firm evidence for the existence of HClOH˙ as a species distinct from Cl˙, that the chemistry attributed to HClOH˙ can be accounted for by other well-established species, and that almost all published mechanisms that include reactions of HClOH˙ violate the principle of detailed balancing. More than 100 publications are identified that violate the principle of detailed balancing with HClOH˙ reactions. Proposals for the participation of HClOH˙ in reaction mechanisms originated in studies of the photochemical peroxydisulfate/chloride reaction; here we provide a revised mechanism that omits HClOH˙, complies with the principle of detailed balancing, and has a minimal number of reaction steps.

Role of Size and Composition on the Design of Superalkalis.

Superalkalis and superhalogens are atomic clusters that mimic the chemistry of alkali and halogen atoms, respectively; the ionization energies of the superalkalis are less than those of alkali atoms, while the electron affinities of superhalogens are larger than those of the halogen atoms. These superions can serve as the building blocks of a new class of supersalts with applications in solar cells, metal-ion batteries, multiferroic materials, and so on. While considerable progress has been made in the design and synthesis of superhalogens, a similar understanding of superalkalis is lacking. Using density functional theory with hybrid exchange-correlation functional and Gaussian basis sets, we have systematically studied the role of size and composition on the properties of two different classes of clusters whose stabilities are governed by the Wade-Mingos polyhedral skeletal electron pair theory. One class belongs to the closo-borane family LimBnXn (m = 1, 2, 3; n = 6, 12; X = H, F, CN), while the other to the Zintl ions Lim[Be@Ge9]. We show that Li3BnXn and Li3[Be@Ge9] clusters are superalkalis with ionization energies as low as 2.84 eV in Li3B6H6. However, contrary to expectation, the ionization energies do not decrease with increasing cluster volume. Instead, ionization energies are linked to the X ligands' electron affinities; the larger the electron affinity, the higher is the ionization energy. The understanding gained here will help in the discovery of superalkalis and, hence, enrich the library of supersalts.

Boosting Selective Nitrogen Reduction via Geometric Coordination Engineering on Single-Tungsten-Atom Catalysts.

Atomic interface regulation that can efficiently optimize the performance of single-atom catalysts (SACs) is a worthwhile research topic. The challenge lies in deeply understanding the structure-properties correlation based on control of the coordination chemistry of individual atoms. Herein, a new kind of W SACs with oxygen and nitrogen coordination (W-NO/NC) and a high metal loading over 10 wt% is facilely prepared by introducing an oxygen-bridged [WO4 ] tetrahedron. The local structure and coordination environment of the W SACs are confirmed by high-angle annular dark-field scanning transmission electron microscopy, X-ray photoelectron spectroscopy, and extended X-ray absorption fine structure. The catalyst shows excellent selectivity and activity for the electrochemical nitrogen reduction reaction (NRR). Density functional theory calculation reveals that unique electronic structures of the N and O dual-coordinated W sites optimize the binding energy of the NRR intermediate, resulting in facilitating the electrocatalytic NRR. This work opens an avenue toward exploring the correlation between coordination structure and properties.

A family of ionic supersalts with covalent-like directionality and unconventional multiferroicity

Ionic crystals composed of elemental ions such as NaCl are non-polar due to directionless ionic bonding interactions. Here, we show that these can develop polarity by changing their building blocks from elemental ions to superalkali and superhalogen cluster-ions, which mimic the chemistry of alkali and halogen atoms, respectively. Due to the non-spherical geometries of these cluster ions, corresponding supersalts form anisotropic polar structures with ionic bonding, yet covalent-like directionality, akin to sp3 hybridized systems. Using density functional theory and extensive structure searches, we predict a series of stable ferroelectric/ferroelastic supersalts, PnH4MX4 (Pn = N, P; M = B, Al, Fe; X = Cl, Br) composed of superalkali PnH4 and superhalogen MX4 ions. Unlike traditional ferroelectric/ferroelastic materials, the cluster-ion based supersalts possess ultra-low switching barrier and can endure large ion displacements and reversible strain. In particular, PH4FeBr4 exhibits triferroic coupling of ferroelectricity, ferroelasticity, and antiferromagnetism with controllable spin directions via either ferroelastic or 90-degree ferroelectric switching.

Evaluating the sensitivity of radical chemistry and ozone formation to ambient VOCs and NO&amp;lt;sub&amp;gt;&amp;lt;i&amp;gt;x&amp;lt;/i&amp;gt;&amp;lt;/sub&amp;gt; in Beijing

Abstract. Measurements of OH, HO2, complex RO2 (alkene- and aromatic-related RO2) and total RO2 radicals taken during the integrated Study of AIR Pollution PROcesses in Beijing (AIRPRO) campaign in central Beijing in the summer of 2017, alongside observations of OH reactivity, are presented. The concentrations of radicals were elevated, with OH reaching up to 2.8×107moleculecm-3, HO2 peaking at 1×109moleculecm-3 and the total RO2 concentration reaching 5.5×109moleculecm-3. OH reactivity (k(OH)) peaked at 89 s−1 during the night, with a minimum during the afternoon of ≈22s-1 on average. An experimental budget analysis, in which the rates of production and destruction of the radicals are compared, highlighted that although the sources and sinks of OH were balanced under high NO concentrations, the OH sinks exceeded the known sources (by 15 ppbv h−1) under the very low NO conditions (&lt;0.5 ppbv) experienced in the afternoons, demonstrating a missing OH source consistent with previous studies under high volatile organic compound (VOC) emissions and low NO loadings. Under the highest NO mixing ratios (104 ppbv), the HO2 production rate exceeded the rate of destruction by ≈50ppbvh-1, whilst the rate of destruction of total RO2 exceeded the production by the same rate, indicating that the net propagation rate of RO2 to HO2 may be substantially slower than assumed. If just 10 % of the RO2 radicals propagate to HO2 upon reaction with NO, the HO2 and RO2 budgets could be closed at high NO, but at low NO this lower RO2 to HO2 propagation rate revealed a missing RO2 sink that was similar in magnitude to the missing OH source. A detailed box model that incorporated the latest Master Chemical Mechanism (MCM3.3.1) reproduced the observed OH concentrations well but over-predicted the observed HO2 under low concentrations of NO (&lt;1 ppbv) and under-predicted RO2 (both the complex RO2 fraction and other RO2 types which we classify as simple RO2) most significantly at the highest NO concentrations. The model also under-predicted the observed k(OH) consistently by ≈10s-1 across all NOx levels, highlighting that the good agreement for OH was fortuitous due to a cancellation of missing OH source and sink terms in its budget. Including heterogeneous loss of HO2 to aerosol surfaces did reduce the modelled HO2 concentrations in line with the observations but only at NO mixing ratios &lt;0.3 ppbv. The inclusion of Cl atoms, formed from the photolysis of nitryl chloride, enhanced the modelled RO2 concentration on several mornings when the Cl atom concentration was calculated to exceed 1×104atomscm-3 and could reconcile the modelled and measured RO2 concentrations at these times. However, on other mornings, when the Cl atom concentration was lower, large under-predictions in total RO2 remained. Furthermore, the inclusion of Cl atom chemistry did not enhance the modelled RO2 beyond the first few hours after sunrise and so was unable to resolve the modelled under-prediction in RO2 observed at other times of the day. Model scenarios, in which missing VOC reactivity was included as an additional reaction that converted OH to RO2, highlighted that the modelled OH, HO2 and RO2 concentrations were sensitive to the choice of RO2 product. The level of modelled to measured agreement for HO2 and RO2 (both complex and simple) could be improved if the missing OH reactivity formed a larger RO2 species that was able to undergo reaction with NO, followed by isomerisation reactions reforming other RO2 species, before eventually generating HO2. In this work an α-pinene-derived RO2 species was used as an example. In this simulation, consistent with the experimental budget analysis, the model underestimated the observed OH, indicating a missing OH source. The model uncertainty, with regards to the types of RO2 species present and the radicals they form upon reaction with NO (HO2 directly or another RO2 species), leads to over an order of magnitude less O3 production calculated from the predicted peroxy radicals than calculated from the observed peroxy radicals at the highest NO concentrations. This demonstrates the rate at which the larger RO2 species propagate to HO2, to another RO2 or indeed to OH needs to be understood to accurately simulate the rate of ozone production in environments such as Beijing, where large multifunctional VOCs are likely present.

Synchronizing chemistry, quantum mechanics and radioactivity in a revolutionary renewed atom model. Part 1: the elements where Z is 1-10 (H, He, Li, Be, B, C, N, O, F, Ne).

The alliance between the reigning quantum mechanical atom model and chemistry still is a difficult one when it comes to an adequate explanation for e.g. the covalent bond, inversion, chirality, or hydrogen bonds. Overruling Rutherford's extrapolation from gold to hydrogen, an atom model is described that provides improved answers to these phenomena while the hybridization principle and the covalent bond are re-defined by giving neutrons a much more prominent role than they have in the reigning quantum mechanical model. It is postulated that a neutron is not just there to assist the strong force in surpassing the repulsive coulombic forces between the protons in the nucleus, but the neutron is the modus operandi of molecular geometry, and as such plays a part in chemical reactivity, bond length and bond strength.

Controlling the Charge Transfer across Thin Dielectric Interlayers

AbstractWhether intentional or unintentional, thin dielectric interlayers can be found in technologies ranging from catalysis to organic electronics. While originally considered as passive decoupling layers, recently it has been shown that they can actively promote charge transfer from the underlying metal to adsorbates. This charging can have profound effects on the surface chemistry of atoms, atomic clusters, and molecules, their magnetic moments, and charge injection at the contacts of organic devices. Yet, controlled studies required to understand the charge transfer process in depth are still lacking. Here, a comprehensive analysis of the phenomenon of charge transfer using the atomically controlled system of pentacene on ultrathin MgO(100) films on Ag(100) is presented. It is shown that the charge transfer process is governed by the charged and uncharged molecular species with distinct energy levels in the first monolayer. The experimental approach applied in this work allows to observe and control their ratio through direct tuning of either the work function or the thickness of the dielectric interlayer.

BDF: A relativistic electronic structure program package.

The BDF (Beijing Density Functional) program package is in the first place a platform for theoretical and methodological developments, standing out particularly in relativistic quantum chemical methods for chemistry and physics of atoms, molecules, and periodic solids containing heavy elements. These include the whole spectrum of relativistic Hamiltonians and their combinations with density functional theory for the electronic structure of ground states as well as time-dependent and static density functional linear response theories for electronically excited states and electric/magnetic properties. However, not to be confused by its name, BDF nowadays comprises also of standard and novel wave function-based correlation methods for the ground and excited states of strongly correlated systems of electrons [e.g., multireference configuration interaction, static-dynamic-static configuration interaction, static-dynamic-static second-order perturbation theory, n-electron valence second-order perturbation theory, iterative configuration interaction (iCI), iCI with selection plus PT2, and equation-of-motion coupled-cluster]. Additional features of BDF include a maximum occupation method for finding excited states of Hartree-Fock/Kohn-Sham (HF/KS) equations, a very efficient localization of HF/KS and complete active space self-consistent field orbitals, and a unique solver for exterior and interior roots of large matrix eigenvalue problems.