Atomic Chains Research Articles

Electronic and spin states at edges of finite p-orbital helical atomic chain.

In connection to the chiral-induced spin selectivity effect, we theoretically analyze the electronic and spin states of edges of a finite p-orbital helical atomic chain with the intra-atomic spin-orbit interaction. This model can host the spin-filtering state in which two up-spins propagate in one direction and two down-spins propagate in the opposite direction without breaking the time-reversal symmetry (TRS). The enhancement of charge modulations concentrated at the edges due to the evanescent states is induced, although the spin density is absent because of the TRS. A Zeeman field at an edge of the atomic chain, which breaks the TRS, yields a finite spin polarization, whose direction depends on the chirality of the molecule. The chirality change induces a reasonable amount of the energy difference, which may provide an insight into the enantioselective adsorption of chiral molecules on the ferromagnetic surface.

Thermal Transport in Nano Structured Carbon Nanotubes and Its Thermal Conductance

We have studied thermal transport in nano-structured carbon nanotubes and have calculated its thermal conductance using the nonequilibrium Green’s function method. The thermal conductance of carbon nanotubes linearly depended on the width of the unzipped part of the carbon nanotube but exponentially decayed and then converged to a finite value of the unzipped length increased. But characteristics are unusual to common bulk materials but are universal to nano materials of nanotube and graphene like structures. An exponentially decayed thermal conductance with the length was found at interfaces. Electronic conductance was found to show an exponential thermal transport in carbon nanotubes showed features distinctly different from those in common bulk materials. Carbon nanotubes have been found strong structural imperfections; their thermal conductance exhibited unexpectedly perfect linear scaling behavior as the width of the unzipped part changed. As the unzipped length increased, thermal conductance exponentially decreased by the one dimensional atomic chain model. The obtained results were found in good agreement with previous results.

Chemisorption of gas atoms on one-dimensional transition-metal halides

We study computationally the bonding of hydrogen and oxygen to one-dimensional materials with the formula XY3, where X represents Ti, Zr, or Hf and Y represents a halogen atom Cl, Br, or I. The materials consist of chains of transition metal atoms surrounded by halogen atoms with a three-fold rotation symmetry. The chemisorption leads to a reduction in the number of d-electrons in the materials accompanied by significant changes in Fermi energy. The chemisorption energies are seen to correlate with the work functions of the clean systems supporting the view that electron transfer plays a major role in the bonding.

The low-LET radiation contribution to the tumor dose in diffusing alpha-emitters radiation therapy.

Diffusing alpha-emitters Radiation Therapy ("Alpha DaRT") is a new technique that enables the use of alpha particles for the treatment of solid tumors. Alpha DaRT employs interstitial sources carrying a few Ci of Ra below their surface, designed to release a chain of short-lived atoms (progeny of Ra) which emit alpha particles, along with beta, Auger, and conversion electrons, x- and gamma rays. These atoms diffuse around the source and create-primarily through their alpha decays-a lethal high-dose region measuring a few millimeters indiameter. While previous studies focused on the dose from the alpha emissions alone, this work addresses the electron and photon dose contributed by the diffusing atoms and by the atoms remaining on the source surface, for both a single Alpha DaRT source and multi-source lattices. This allows to evaluate the low-LET contribution to the tumor dose and tumor cell survival, and demonstrate the sparing of surrounding healthytissue. The low-LET dose is calculated using the EGSnrc and FLUKA Monte Carlo (MC) codes. We compare the results of a simple line-source approximation with no diffusion to those of a full simulation, which implements a realistic source geometry and the spread of diffusing atoms. We consider two opposite scenarios: one with low diffusion and high Pb leakage, and the other with high diffusion and low leakage. The low-LET dose in source lattices is calculated by superposition of single-source contributions. Its effect on cell survival is estimated with the linear quadratic model in the limit of low doserate. For sources carrying 3 Ci/cm Ra arranged in a hexagonal lattice with 4mm spacing, the minimal low-LET dose between sources is Gy for the two test cases and is dominated by the beta contribution. The low-LET dose drops below 5Gy mm away from the outermost source in the lattice with an effective maximal dose rate of Gy/h. The accuracy of the line-source/no-diffusion approximation is for the total low-LET dose over clinically relevant distances (2-4mm). The low-LET dose reduces tumor cell survival by a factor of . The low-LET dose in Alpha DaRT can be modeled by conventional MC techniques with appropriate leakage corrections to the source activity. For 3 Ci/cm Ra sources, the contribution of the low-LET dose can reduce cell survival inside the tumor by up to two orders of magnitude. The low-LET dose to surrounding healthy tissue is negligible. Increasing source activities by a factor of 5 can bring the low-LET dose itself to therapeutic levels, in addition to the high-LET dose contributed by alpha particles, leading to a "self-boosted" Alpha DaRT configuration, and potentially allowing to increase the latticespacing.

A Proof of Finite Crystallization via Stratification

We devise a new technique to prove two-dimensional crystallization results in the square lattice for finite particle systems. We apply this strategy to energy minimizers of configurational energies featuring two-body short-ranged particle interactions and three-body angular potentials favoring bond-angles of the square lattice. To each configuration, we associate its bond graph which is then suitably modified by identifying chains of successive atoms. This method, called stratification, reduces the crystallization problem to a simple minimization that corresponds to a proof via slicing of the isoperimetric inequality in ℓ1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\ell ^1$$\\end{document}. As a byproduct, we also prove a fluctuation estimate for minimizers of the configurational energy, known as the n3/4\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$n^{3/4}$$\\end{document}-law.

Morphologically Tunable Rectangular Platelets Self-Assembled from Diblock Molecular Brushes Containing Azopyridine Pendants.

Two-dimensional (2D) platelet structures are of growing importance as building blocks for the preparation of optical and electrical devices. However, the creation of morphologically tunable rectangular platelets through polymer self-assembly still remains a challenge. Herein, we describe a rational strategy for the fabrication of 2D rectangular platelets by stacking azopyridine-containing diblock molecular brushes in two dimensions in a selective solvent. Amphiphilic PEG-co-(PtBA-g-PAzoPy) DMBs with poly(ethylene glycol) (PEG) block, poly(t-butyl acrylate) (PtBA) backbone, and poly(6-(4-(4-pyridyazo)phenoxy)-hexyl methacrylate) (PAzoPy) brush were synthesized by sequential reversible addition-fragmentation chain transfer polymerization and atom transfer radical polymerization. Various rectangular platelets were obtained via the solution self-assembly of PEG-co-(PtBA-g-PAzoPy) through a heating-cooling-aging process in which the morphology and size of platelets could be controlled by adjusting the composition of DMBs as well as the solvent polarity. In addition, we investigated the metal chelation ability and H-bonding-assisted co-assembly capability of PEG-co-(PtBA-g-PAzoPy). The results displayed that 2D hybrids and flower-like platelets were formed, respectively. Our study presents an efficient method to fabricate rectangular platelets with tunable morphologies.

Topological data analysis of TEM-based structural features affecting the thermal conductivity of amorphous Ge

Compared to crystalline materials, amorphous materials lack periodicity and exhibit distinct thermal and lattice vibration properties. Hence, analyzing atomic networks in the transmission electron microscopy (TEM) images of amorphous materials is challenging. In this study, we employ topological data analysis (TDA) and principal component analysis (PCA) to extract structural features from the TEM images of amorphous germanium (a-Ge) and analyze its atomic networks. Our findings demonstrate that the thermal conductivity of a-Ge is influenced by larger atomic rings with more vertices, which facilitates the heat transfer through longer atomic chains and results in a higher thermal conductivity. A comparison of the experimental and simulation data confirms the non-random nature of the atomic arrangements in a-Ge. We propose herein an approach that employs the TDA to identify and analyze the atomic networks in amorphous materials, establishing connections to their thermal properties. This study enhances our understanding of amorphous materials and paves a way for tailored material design and engineering to achieve the desired thermal properties.

Microscopic mechanism of plasmon-mediated photocatalytic H2 splitting on Ag–Au alloy chain

Alloy nanostructures supporting localized surface plasmon resonances has been widely used as efficient photocatalysts, but the microscopic mechanism of alloy compositions enhancing the catalytic efficiency is still unclear. By using time-dependent density functional theory (TDDFT), we analyze the real-time reaction processes of plasmon-mediated H2 splitting on linear Ag–Au alloy chains when exposed to femtosecond laser pulses. It is found that H2 splitting rate depends on the position and proportion of Au atoms in alloy chains, which indicates that specially designed Ag–Au alloy is more likely to induce the reaction than pure Ag chain. Especially, more electrons directly transfer from the alloy chain to the anti-bonding state of H2, thereby accelerating the H2 splitting reaction. These results establish a theoretical foundation for comprehending the microscopic mechanism of plasmon-induced chemical reaction on the alloy nanostructures.

Edge Magnetism in MoS2 Nanoribbons: Insights from a Simple One-Dimensional Model.

Edge magnetism in zigzag nanoribbons of monolayer MoS2 has been investigated with both density functional theory and a tight-binding plus Hubbard (TB+U) Hamiltonian. Both methods revealed that one band crossing the Fermi level is more strongly influenced by spin polarization than any other bands. This band originates from states localized on the sulfur edge of the nanoribbon. Its dispersion closely resembles that of the energy branch obtained in a linear chain of atoms with first-neighbor interaction. By exploiting this resemblance, a toy model has been designed to study the energetics of different spin configurations of the nanoribbon edge.

Unveiling the structure of calcium borate glass by neutron diffraction, MAS-NMR, Raman and first-principles calculations

Calcium borate glass is a challenging system, due to the rich variety of borate units and alterable boron coordination number, and hence they are also of particular interest for academic study. In this study, neutron diffraction, solid-state magic angle spinning nuclear magnetic resonance (MAS-NMR) and Raman spectroscopy were combined with first-principles calculations, experience potential structure refinement (EPSR) simulations to investigate the structure of xCaO·(1-x)11B2O3 glass. Property data such as density and glass transition temperature were also measured to study the impact of structural changes on the properties of glasses. The structure of calcium borate glass was analyzed using various methods including structural unit, atomic pair bond length, coordination number, ring structure, chain structure and cavity distribution. Most notably, the atomic labeling method plays a key role in the structural analysis process. Through this method some new conclusions were obtained. For example, the increase of CaO content mainly leads to the conversion of BO to NBO in the glass structure, and has little effect on the content of BO3 and BØ4-. This result further leads to an increase in Ca-NBO interactions. Interestingly, the bond length distribution of Ca-NBO and B-NBO is shorter than that of Ca-BO and B-BO, so the glass structure becomes denser. The structural reason why the density of calcium borate glass is less than the crystal density was also revealed. This study contributes to unveiling the structure of calcium borate glass and exploring the correlation between the structure and properties of calcium borate glass, which provides a valuable reference for developing more valuable amorphous materials.

Electronic structure and intrinsic mobilities of one-dimensional CuO2 atomic wires: A first-principles study

Herein, the electronic structure and intrinsic carrier mobility of the one-dimensional CuO2 atomic chain were studied by first-principles calculations. The band structure of the CuO2 atomic chain was obtained using the HSE06 hybrid functional with spin polarization. The results show that the band gap and hole effective mass of antiferromagnetic (ferromagnetic) CuO2 were 1.42 (0.38) eV and 1.53 (0.81) m0, respectively. The magnetism in CuO2 mainly originates from O atoms, consistent with the experiment, and the magnetic moment of these O atoms in the antiferromagnetic (ferromagnetic) state was ±0.58 (+0.41) μB. The intrinsic carriers of CuO2 have relatively high hole mobility (318 cm2 V−1 s−1) and extremely low electron mobility. Combined with the phonon dispersion calculation, the CuO2 atomic chain is an excellent and structurally stable p-type one-dimensional semiconductor material. Our work is expected to provide useful guidance for thermal transport materials containing CuO2 atomic chain substructure.

Design, Molecular Docking, Synthesis and Evaluation of Xanthoxylin Hybrids as Dual Inhibitors of IL‐6 and Acetylcholinesterase for Alzheimer’s Disease

AbstractBackgroundIL‐6 and AChE play a pivotal role in progression of AD, it is hypothesised that simultaneous inhibition of IL‐6 and AChE may prove as an effective strategy for treatment of AD. Therefore, the present study is undertaken to design novel molecules capable of acting as dual inhibitors of IL‐6 and AChE. Literature review reveals that xanthoxylin and a disubstituted amines or a carbamoyl amines are pharmacophores for IL‐6 and AChE inhibition, respectively.MethodXanthoxylin is coupled with various disubstituted amines or carbamoyl amines through alkyl linkers of different lengths (1‐4 carbon atoms) to design two series of 80 compounds. All designed compounds were docked into AChE to identify the best fit compounds for synthesis and evaluation of AChE inhibitory activity. The compounds showing >45% inhibition of EeAChE are selected for evaluation of IL‐6 and butyrylcholinesterase (BuChE) inhibitory activities. The compound found to be most potent against AChE, BuChE and IL‐6 inhibition was finally evaluated in vivo using STZ‐induced amnesia model in mice at three doses (0.2, 0.4 and 0.8 mg/kg).ResultCompound K13g is found to be the most potent inhibitor of EeAChE, BuChE and IL‐6. It is further evaluated in vivo, wherein it shows dose‐dependent effects. It is observed to be less active at lower doses, but completely reversed the STZ‐induced memory deficit at 0.8 mg/kg.ConclusionThe findings suggest that a compound having a xanthoxylin moiety connected to a piperazine ring through a three‐carbon atom chain may provide a useful template for the development of new chemical entities effective against AD.

Nanoscale Insights into the Mechanical Behavior of Interfacial Composite Structures between Calcium Silicate Hydrate/Calcium Hydroxide and Silica

The failure of the interfacial transition zone has been identified as the primary cause of damage and deterioration in cement-based materials. To further understand the interfacial failure mechanism, interfacial composite structures between the main hydration products of ordinary Portland cement (OPC), calcium silicate hydrate (CSH) and calcium hydroxide (Ca(OH)2), and silica (SiO2) were constructed while considering their anisotropy. Afterwards, uniaxial tensile tests were conducted using molecular dynamics (MD) simulations. Our results showed that the interfacial zones (IZs) of interfacial composite structures tended to have relatively lower densities than those of the bulk, and the anisotropy of the hydration products had almost no effect on the IZ being a low-density zone. Interfacial composite structures with different configurations exhibited diverse nanomechanical behaviors in terms of their ultimate strength, stress–strain relationship and fracture evaluation. A higher strain rate contributed to a higher ultimate strength and a more prolonged decline in the residual strength. In the interfacial composite structures, both CSH and Ca(OH)2 exhibited ruptures of the Ca-O bond as the primary atomic pair during the tensile process. The plastic damage characteristics of the interfacial composite structures during the tensile process were assessed by analyzing the normalized number of broken Ca-O bonds, which also aligned with the atomic chain break characteristics evident in the per-atom stress map.

Carbon nanobracelets

Carbon-based cyclic molecules with alternating polycyclic regions and double carbon chains referred to as carbon nanobracelets are studied using spin-polarized density functional theory (DFT) calculations with PBE functional. Optimized structure of considered nanobracelets consisting of 1–5 identical monomers with and without hydrogen atoms at the edge of polycyclic regions is found to have highest possible symmetry and bond length alternation in chains. Nanobracelets consisting of odd number of monomers have lower HOMO energy, greater HOMO-LUMO gap and greater bond length variation in the carbon atomic chains than nanobracelets with even number of monomers.

Driving mechanisms of high-cetane number, synthetic fuel autoignition: The case of OME[formula omitted

Oxymethylene dimethyl ethers (CH3O(CH2O)xCH3 or OMEx) are potential synthetic substitutes of diesel and jet fuel that can be acquired through CO2 recycling and have the unique “clean” feature that they do not contain C-C bonds in their atom chain, but only C-O, and therefore can combust without soot. Also, they present favourable ignition characteristics and high cetane numbers. In order to determine ignition control strategies, the dominant oxidation pathways must be identified. To this end, autoignition of OME2−4/air mixtures is studied using the tools of Computational Singular Perturbation algorithm. It is shown that as the length of the atom chain x increases, ignition delays become shorter. This is because, at the very early stages of the process, H-abstraction and fuel break-up reactions realize in a larger number of ways for larger x. The process develops first through a chemical runaway that tends to slow-down autoignition and then through a thermal runaway that tends to speed-up autoignition at a progressively stronger rate. It is shown that the total heat release is independent of x, although the ignition delay becomes shorter with increasing x. The two stable intermediates H2O2 and CH2O are shown to shorten ignition delays, when used as additives in the initial mixtures. It is demonstrated that OMEx synthetic fuels offer the capability of soot-less combustion, combined with ignition control.

Masked alkynes for synthesis of threaded carbon chains

Polyynes are chains of sp1 carbon atoms with alternating single and triple bonds. As they become longer, they evolve towards carbyne, the 1D allotrope of carbon, and they become increasingly unstable. It has been anticipated that long polyynes could be stabilized by supramolecular encapsulation, by threading them through macrocycles to form polyrotaxanes—but, until now, polyyne polyrotaxanes with many threaded macrocycles have been synthetically inaccessible. Here we show that masked alkynes, in which the C≡C triple bond is temporarily coordinated to cobalt, can be used to synthesize polyrotaxanes, up to the C68 [5]rotaxane with 34 contiguous triple bonds and four threaded macrocycles. This is the length regime at which the electronic properties of polyynes converge to those of carbyne. Cyclocarbons constitute a related family of molecular carbon allotropes, and cobalt-masked alkynes also provide a route to [3]catenanes and [5]catenanes built around cobalt complexes of cyclo[40]carbon and cyclo[80]carbon, respectively.

Tuning of excitons in phosphorene atomic chains

An universal scaling between the exciton binding energy and quasiparticle (QP) band gap was first discovered in two-dimensional (2D) semiconductors such as graphene derivatives, various transition materials dichalcogenides, and black phosphorus (Choi et al 2015 Phys. Rev. Lett. 115 066403; Jiang et al 2017 Phys. Rev. Lett. 118 266401), and later extended to quasi one-dimensional (1D) systems such as carbon nanotubes and graphene nanoribbons. In this work we study the excitonic states in phosphorene atomic chains by using the exact diagonalization method and show that the linear scaling between the exciton binding energy (Ex ) and QP shift () can be easily tuned by the dielectric environment. In the presence of weak screening, Ex is seen to increase with and exhibits a similar scaling as those 2D materials. As the screening becomes stronger, however, the dependence is found to be reversed, i.e. Ex now decreases when increases. More interestingly, we also reveal that Ex may even become nearly constant, independent on the system dimension and when the screening reaches a certain strength. These abnormal scaling relations are attributed to the complex nature of excitons in the strongly correlated 1D system.

Half-metallic magnetism in 2D MX2 (M = V, Cr, Mn, and Fe; X = S, Se, and Te) intercalated with 1D MX chains

Intercalation has attracted considerable attention due to its extensive ability to modify the electronic, optical, and magnetic properties of two-dimensional (2D) layered nanomaterials. Typically, dispersed atoms or molecules are inserted into the van der Waals gap of the 2D materials. Recently, Guo et al. experimentally reported the novel VS2–VS superlattice, where the intercalation takes the form of atomic chain arrays. In this study, we employed the first-principles calculations based on density functional theory to investigate a series of analogous 2D MX2–MX–MX2 nanomaterials, which, consisting of 2D transition metal dichalcogenide bilayers, intercalated with a one-dimensional transition metal chalcogenide MX chain array, forming a hotdog-like structure. Some of the 2D MX2–MX–MX2 are thermally and dynamically stable, suggesting their potential for experimental fabrication similar to VS2–VS–VS2. MnS2–MnS–MnS2 and MnSe2–MnSe–MnSe2 have been found to exhibit ferromagnetic half-metallic properties. In addition, VSe2–VSe–VSe2, CrS2–CrS–CrS2, and CrSe2–CrSe–CrSe2 have been found to be thermally and dynamically stable. Under appropriate external stress, doping, or bias, they could become ferromagnetic half-metals, revealing their potential for spintronic applications.

Zeno Regime of Collective Emission: Non-Markovianity beyond Retardation.

To build up a collective emission, the atoms in an ensemble must coordinate their behavior by exchanging virtual photons. We study this non-Markovian process in a subwavelength atom chain coupled to a one-dimensional (1D) waveguide and find that retardation is not the only cause of non-Markovianity. The other factor is the memory of the photonic environment, for which a single excited atom needs a finite time, the Zeno regime, to transition from quadratic decay to exponential decay. In the waveguide setup, this crossover has a time scale longer than the retardation, thus impacting the development of collective behavior. By comparing a full quantum treatment with an approach incorporating only the retardation effect, we find that the field memory effect, characterized by the population of atomic excitation, is much more pronounced in collective emissions than that in the decay of a single atom. Our results maybe useful for the dissipation engineering of quantum information processings based on compact atom arrays.

Anonymous Pattern Molecular Fingerprint and its Applications on Property Identification.

Molecular fingerprints are significant cheminformatics tools to map molecules into vectorial space according to their characteristics in diverse functional groups, atom sequences, and other topological structures. In this paper, we investigate a novel molecular fingerprint Anonymous-FP that possesses abundant perception about the underlying interactions shaped in small, medium, and large-scale atom chains. In detail, the possible atom chains from each molecule are sampled and extended as anonymous atom chains using an anonymous encoding manner. After that, the molecular fingerprint Anonymous-FP is embedded into vectorial space in virtue of the Natural Language Processing technique PV-DBOW. Anonymous-FP is studied on molecular property identification via molecule classification experiments on a series of molecule databases and has shown valuable advantages such as less dependence on prior knowledge, rich information content, full structural significance, and high experimental performance. During the experimental verification, the scale of the atom chain or its anonymous pattern is found significant to the overall representation ability of Anonymous-FP. Generally, the typical scale r = 8 could enhance the molecule classification performance, and specifically, Anonymous-FP gains the classification accuracy to above 93% on all NCI datasets.