Atomistic Study Research Articles

Ab initio investigation of hot electron transfer in CO2 plasmonic photocatalysis in the presence of hydroxyl adsorbate.

Photoreduction of carbon dioxide (CO2) on plasmonic structures is of great interest in photocatalysis to aid selectivity. While species commonly found in reaction environments and associated intermediates can steer the reaction down different pathways by altering the potential energy landscape of the system, they are often not addressed when designing efficient plasmonic catalysts. Here, we perform an atomistic study of the effect of the hydroxyl group (OH) on CO2 activation and hot electron generation and transfer using first-principles calculations. We show that the presence of OH is essential in breaking the linear symmetry of CO2, which leads to a charge redistribution and a decrease in the OCO angle to 134°, thereby activating CO2. Analysis of the partial density of states (pDOS) demonstrates that the OH group mediates the orbital hybridization between Au and CO2 resulting in more accessible states, thus facilitating charge transfer. By employing time-dependent density functional theory (TDDFT), we quantify the fraction of hot electrons directly generated into hybridized molecular states at resonance, demonstrating a broader energy distribution and an 11% increase in charge-transfer in the presence of OH groups. We further show that the spectral overlap between excitation energy and plasmon resonance plays a critical role in efficiently modulating electron transfer processes. These findings contribute to the mechanistic understanding of plasmon-mediated reactions and demonstrate the importance of co-adsorbed species in tailoring the electron transfer processes, opening new avenues for enhancing selectivity.

Full-band atomistic study of electron-phonon interaction in carbon nanotubes

Full-band atomistic study of electron-phonon interaction in carbon nanotubes

Atomistic study on dislocation emission from segregated grain boundaries in high-entropy alloys

Atomistic study on dislocation emission from segregated grain boundaries in high-entropy alloys

Atomistic modelling and NMR studies reveal that gallium can target the ferric PQS uptake system in P. aeruginosa biofilms.

Intravenous gallium nitrate therapy is a novel therapeutic strategy deployed to combat chronic Pseudomonas aeruginosa biofilm infections in the lungs of cystic fibrosis (CF) patients by interfering with iron (Fe3+) uptake. The therapy is a source of Ga3+, which competes with Fe3+ for siderophore binding, subsequently disrupting iron metabolism and inhibiting biofilm proliferation in vivo. It was recently demonstrated that the Pseudomonas quinolone signal (PQS) can chelate Fe3+ to assist in bacterial iron uptake. However, it is unknown whether exogenous gallium also targets [Fe(PQS)3] uptake, which, in turn, would extend the mechanism of gallium therapy beyond siderophore competition, potentially supporting use of the therapy against P. aeruginosa mutants deficient in siderophore uptake proteins. To that end, the thermodynamic feasibility of iron-for-gallium cation exchange into [Fe(PQS)3] was evaluated using quantum chemical density functional theory (DFT) modelling and verified experimentally using 1H nuclear magnetic resonance (NMR). We demonstrate here that Ga3+ can strongly bind to three PQS molecules and, furthermore, displace and substitute Fe3+ from the native chelate pocket within PQS complexes, through a Trojan horse mechanism, retaining the key structural features present within the native ferric complex. As such, [Fe(PQS)3] complexes, in addition to ferric-siderophore complexes, represent another target for gallium therapy.

Engulfment and Pushing of Cylindrical Liquid Nano-Inclusion by Advancing Crystal/Melt Interface: An Atomistic Simulation Study.

We reported a molecular dynamics (MD) simulation study of an advancing pure Al(100)/melt interface that encounters a foreign immiscible liquid Pb cylindrical nano-inclusion. When the advancing interface approaches the inclusion, the interface may engulf, push to an extent and then engulf or push the nano-inclusion away from the solidifying phase depending on the velocity of the interface. Here, we investigated cylindrical liquid Pb nano-inclusion pushing or engulfment by a growing crystal Al that strongly depends on the velocity of the crystal/melt interface, and a critical velocity (vc) is deduced. If the velocity of the interface is less than vc, then the inclusion is pushed and engulfed otherwise. The relationship between vc and the radius of the nano-inclusion is expressed using a power function that agrees well with the previous studies. For velocity above the vc, the crystal/melt interface plays a vital role; it hinders the matrix atoms from setting below the cylindrical nano-inclusion due to insufficient mass transfer below the inclusion, resulting in the engulfment.

Atomistic study on the origins of the anisotropic lithiation behaviors of the silicon anode using the reactive force field based molecular dynamics simulations

We employed the Reactive-Force-field (ReaxFF) based molecular dynamics simulations to investigate the lithiation mechanisms and anisotropic lithiation behaviors of the Si-based anode during the lithiation processes. In order to accurately predict the relative lithiation kinetics on different surface facets of c-Si, we have developed new ReaxFF parameters for the Li-Si system based on first-principles calculations. Our results demonstrated that the lithiation kinetics on the Si(110) and (112) surfaces manifestly outperformed those occurred on the Si(100) and (111) surfaces. The lithiation reactions on the Si(110) and (112) surfaces tend to proceed through a ledge mechanism involving the layer-by-layer peeling of the {111} atomic facets. However, the lithiation reaction on the Si(100) surface is more likely to occur via the layer-by-layer etching of the {100} atomic facets. The discrepancy in the lithiation kinetics among the c-Si(100), (110) and (112) substrates was mainly ascribed to the variation in the compressive stresses that developed within the phase boundary upon lithiation. Regarding the Si(111) surface, the significantly slower lithiation kinetics than other surface facets were primarily attributed to the presence of a considerably larger barrier for Li insertion into the subsurface region to initiate the lithiation reaction. Furthermore, the order of the energy barriers for Li insertion into different c-Si surfaces was determined as follows: Si(111)>>(100)>(110)>(112), indicating that Li atoms tend to migrate into c-Si predominantly through the (110) and (112) surfaces upon lithiation. Consequently, lithiation reactions would occur majorly on the (110) and (112) surfaces due to the much lower compressive stresses that developed within the phase boundary and smaller Li insertion barriers than other surface facets, resulting in the observed anisotropic lithiation behaviors of the c-Si nanomaterials.

The effect of atomic hydrogen on the behavior of a single dislocation of 〈111〉{112} in bcc tungsten: Atomistic study

Tungsten (W) has been widely studied and spotlighted as a plasma-facing material (PFM) in the extreme environment of nuclear fusion due to its excellent physical properties. It is important to investigate the effect of hydrogen on the material behavior of tungsten as it was used in the hydrogen-rich fusion environment. Solute hardening is a typical phenomenon and it is traditionally understood by dragging or pinning effect when hydrogen atoms act like solute atoms that impede dislocation motion. On the other hand, there were several experimental studies reporting softening associated with enhanced dislocation activity, either by easy nucleation or increased mobility, or both. In order to better understand how the effect of hydrogen on mechanical behavior of W, the authors conducted molecular dynamics simulations on dislocation mobility with different dislocation types, hydrogen concentrations, stress, and temperature. At high concentration of 1 at.%, H atoms are often strongly clustered around a dislocation core and produce a super-pinning effect in that both edge and screw started to move at a stress far beyond Peierls stress. This critical stress reduces with temperature increase, and thermally assisted kink or jog formation helps a dislocation escape from the H-cloud trapping. At a low concentration of 0.01-0.1 at.% or a high concentration of 1 at.% without super-pinning, hydrogen dragging barely appeared with a screw dislocation, and the intrinsic lattice resistance dominated the motion of a screw. For an edge dislocation under the same condition, an appreciable reduction in mobility was observed with the increase of H concentration at a low temperature of 300 K and this change in mobility becomes inconspicuous for higher temperatures. In conclusion, this study predicts the hardening of W at a high H concentration of 1 at.% due to dislocation trapping at the H cluster.

Influence of surface facets on the electronic structure of silicon nanowires and slabs from atomistic calculations

Fabrication of modern solid-state devices demands precise control of shape and dimensions, which requires an accurate knowledge of the role that surfaces play in such devices. To contribute to the understanding of surface effects on silicon nanowires, we present an atomistic study of the electronic properties of silicon nanostructures exhibiting surface facets over the (100), (110), (111), and (112) crystallographic planes. We calculate the electronic structure of slabs in such a way that the effect of individual facets may be observed. Subsequently, we determine the electronic structure of nanowires grown along the [100], [110], [111], and [112] directions, with surfaces defined by a combination of the mentioned facets. Our nanowires comprise diameters ranging from 1 to 6.7 nm and structures with more than 1000 atoms. We discuss the band structure, the relation between direct and indirect bandgaps, and the density of states. We base our calculations on semiempirical pseudopotentials where we implement complex potentials to describe passivants. We find that there is a transition from direct to indirect gap for the [111] direction at approximately 2 nm and that the difference between the direct and indirect gap may reach more than 300 meV depending on the diameter. We show that the occurrence of a direct bandgap is favored by the presence of the (100) facet and that it is related to a higher surface density of states. Conversely, we find that the (111) facet is the most inert surface type with a lower surface density of states.

Transformation- and twinning-induced plasticity in phase-separated bcc Nb-Zr alloys: an atomistic study

Several high-temperature body-centered cubic (bcc) structural materials such as Nb-, Zr- and Ti-based alloys undergo phase separation, which is a second-order phase transformation, whereby the host lattice decomposes into distinct bcc domains with different compositions. Using atomistic simulations, we studied the high-strain-rate response of bcc-forming Nb–xZr (x = 0, 25, 50 at.%) alloys. To induce phase separation in our starter alloy, we first employed hybrid Monte Carlo/Molecular Dynamics simulations in single crystals of Nb–xZr at 1000 K. Subsequently, these crystals were deformed along different crystallographic orientations (⟨001⟩\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\langle 001\\rangle$$\\end{document}, ⟨110⟩\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\langle 110\\rangle$$\\end{document} and ⟨111⟩\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\langle 111\\rangle$$\\end{document}) at a strain rate of 10+8s-1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$10^{+8} s^{-1}$$\\end{document}, to investigate orientation dependent mechanical response. The phase-separated Nb–xZr microstructures exhibited distinct bcc domains enriched in either Zr or Nb. Notably, Nb-50 at.%Zr contained coarser Zr-domains compared to Nb-25 at.%Zr. The Zr-rich domains acted as “soft” inclusions, resulting in reduced peak strengths in the following order: pure Nb (Nb-0 at.%Zr) > Nb-25 at.%Zr > Nb-50 at.%Zr. This implies that phase separation causes softening in Nb–xZr. We also discovered two deformation pathways that depended on the crystallographic orientation: (i) For deformation along ⟨110⟩\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\langle 110\\rangle$$\\end{document} and ⟨111⟩\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\langle 111\\rangle$$\\end{document} directions: Elastic deformation was followed by dislocation plasticity on {110}⟨111⟩\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\{110\\}\\langle 111\\rangle$$\\end{document} slip systems; and (ii) For deformation along ⟨001⟩\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\langle 001\\rangle$$\\end{document} direction: Elastic deformation was followed by the formation of a volumetric fcc structure, twinning on {112}⟨111⟩\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\langle 111\\rangle$$\\end{document} system, and the formation fcc-phase at the twin/matrix interfacial regions. This was ultimately accompanied by dislocation plasticity on {110}⟨111⟩\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\{110\\}\\langle 111\\rangle$$\\end{document} slip system. The bcc→\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\rightarrow$$\\end{document}fcc displacive transformation facilitated {112}⟨111⟩\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\langle 111\\rangle$$\\end{document} twinning when Nb–xZr was deformed along ⟨001⟩\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\langle 001\\rangle$$\\end{document}. Our investigation shows that softening of bcc alloys can result from a coupling of mechanisms involving local solute segregation, displacive phase transformation and twinning occurring across multiple slip planes.

Design and fabrication of berberine-loaded electrospun nanofibers as the analgesic and anti-injury scaffold

In the current study, we fabricated an analgesic and anti-injury scaffold nanofibrous scaffold based on berberine-loaded electrospun nanofibers. First off, we applied simulation studies using Material Studio software and Condensed-phase Optimized Molecular Potentials for Atomistic Simulation Studies (COMPASS III) forcefield to assess the interactions between the components of the structure. Then, the electrospinning method was used to synthesize the nanofibers and the nanofibers were characterized using SEM imaging, Liquid displacement method, release kinetics, DPPH assay kit, and MTT assay kit. The results of simulation studies revealed that the non-separation of berberine molecules from the polymer indicates the attractive interaction between the berberine and the PVP polymer and has created an interwoven structure. The findings of molecular dynamics are consistent with the results obtained from experimental data. Therefore, molecular dynamics simulation can be used as a virtual laboratory in research involving berberine and PVP polymer. The characterizations showed that the nanofibers are uniform, without any deformity and bead, with smooth surfaces. Moreover, the addition of Ber in different concentrations did not alter the structure of nanofibers. The porosity of the nanofibrous scaffolds was in the range of 50–70 %. The DPPH radical scavenging showed a dose-dependent antioxidant activity. MTT assay showed that the nanofibers were biocompatible. The results implied that the fabricated berberine-loaded electrospun nanofibers possess promising properties and can be applied as an analgesic and anti-injury scaffold.

Atomistic and continuum study of interactions between super-screw dislocations and coherent twin boundaries in [formula omitted]-structured [formula omitted

Informed by previous experimental observations, this study employed a combination of molecular dynamics simulations and dislocation continuum theory to investigate the interplay of super-screw dislocations and coherent twin boundary (CTB) in Ni3Al. The results reveal multiple interaction mechanisms depending on both the applied stress and the pathway for dislocation gliding. A continuum model framework has been developed to quantitatively evaluate the critical shear stress necessary for the CTB to accommodate dislocations along different pathway with the effects of anti-phase boundary (APB) and Complex Stacking fault (CSF) considered. The critical shear stress exhibits a significant inverse dependence on the quantity of dislocations, rendering it unsuitable as a measure of twin boundary strength. Instead, the resistant force of the CTB against all gliding dislocations is suggested as a more appropriate metric for quantifying its strength. This enables a direct comparison of the twin boundary strength between Ni and Ni3Al containing different amounts of Shockley dislocations, thereby extending its applicability to a wider range of materials. Our work offers new mechanistic insights critical for understanding and quantitative analysis of the interplay of super-dislocations and micro twining in nickel-based superalloys.

Insights into the influence of Ni4Ti3 precipitates and martensite transformation on the glide of a[100] dislocation in austenitic NiTi alloys: an atomistic simulation study

Dislocation-dominated plastic deformation in austenitic NiTi alloys is highly detrimental and it could be suppressed by precipitation of Ni4Ti3. Additionally, at a certain temperature range, not only Ni4Ti3 precipitate but also the B19’ martensite produced from stress-induced martensitic transformation may prevent dislocation glide in austenitic NiTi alloys. In order to shed further light on this issue, four atomic configurations were constructed using an edge dislocation (a [100]) and two Ni4Ti3 precipitate variants (precipitate-V1 and precipitate-V2) to investigate dislocation glide in austenite containing Ni4Ti3 precipitate under shear at temperatures of 500 K or 700 K. As a result, all configurations at 500 K undergo the shear-induced martensitic transformation, producing B19’ martensite that impedes dislocation glide. And at 700 K, dislocation was pinned by precipitate or distortion zones caused by the superposition of strain field of precipitate and dislocation, without martensitic transformation. Furthermore, it was proven that precipitate-V1 impedes dislocation glide more strongly than precipitate-V2 at both temperatures of 500K and 700 K. It was attributed to the different in spatial relative location between the precipitate and dislocation and explained by the Orowan dislocation-precipitate bypass stress. Finally, three strategies for achieving high shear fatigue resistance in NiTi shape memory alloys were proposed based on these findings.

Atomistic study on the effect of the size of diamond abrasive particle during polishing of stainless steel

Nanofinishing or polishing helps to reduce surface roughness, which further improves both the optical and chemical properties of engineering materials. During the polishing of any engineering material, the size of abrasive particles plays a significant role in efficient polishing. In this paper, stainless steel 304 (or SS304) is selected for polishing through diamond abrasives with varying particle sizes using molecular dynamics simulations (MDS). It is found that the diamond abrasive particle initially causes elastic deformation due to the attractive force between the abrasive particle and the workpiece surface. As the size of the abrasive particle increases, plastic deformation occurs by spreading the dislocations on the surface only, which helps to annihilate the dislocations after polishing. It is revealed that the smaller abrasive particles (<3 nm) get trapped due to strong chemical bonding with the surface of the workpiece, and the abrasive particles start depositing on the workpiece instead of material removal. In this paper, it is proposed that an optimum size of abrasive particles is required for a given set of polishing parameters to achieve efficient material removal and minimum surface and subsurface defects. Thus, the present study is worthwhile for efficient polishing or nanocutting of stainless steel through monocrystalline diamond.

Mechanism of thermally-activated prismatic slip in Mg

Prismatic slip of the screw <a> dislocation in magnesium at temperatures ≳ 150 K is understood to be governed by double-cross-slip of the stable basal screw through the unstable prism screw and back to the basal screw, with the activation energy controlled by the formation energy of two basal-basal kinks. However, atomistic studies of the double-kink process predict activation energies roughly twice those derived experimentally. Here, a new mechanism of prism glide is proposed, analyzed theoretically, and demonstrated qualitatively and quantitatively via direct molecular dynamics (MD) simulations. The new mechanism is intrinsically 3d, and involves the nucleation of a single kink at the junction where a 3d prismatic dislocation loop transitions from the basal screw segment to non-screw prismatic character. The relevant kink energies are calculated using recently-developed Neural-Network Potentials (NNPs) for Mg that show good agreement versus DFT for basal and prism <a> dislocations, enabling a parameter-free analytic model for the activation barrier. Direct MD simulations show both operation of the precise proposed mechanism and a stress-dependent activation barrier that agrees reasonably with the analytic model. Predictions of dislocation velocity compare very well with in-situ TEM data, and macroscopic strength versus temperature can also be understood. Overall, the new intrinsically 3d mechanism for dislocation glide due to single kink nucleation rather than double-kink nucleation explains key features of the prismatic slip in Mg and may have broader applicability in other metals where kink nucleation processes control thermally-activated flow.

Comparative Analysis of Conformational Dynamics and Systematic Characterization of Cryptic Pockets in the SARS-CoV-2 Omicron BA.2, BA.2.75 and XBB.1 Spike Complexes with the ACE2 Host Receptor: Confluence of Binding and Structural Plasticity in Mediating Networks of Conserved Allosteric Sites.

In the current study, we explore coarse-grained simulations and atomistic molecular dynamics together with binding energetics scanning and cryptic pocket detection in a comparative examination of conformational landscapes and systematic characterization of allosteric binding sites in the SARS-CoV-2 Omicron BA.2, BA.2.75 and XBB.1 spike full-length trimer complexes with the host receptor ACE2. Microsecond simulations, Markov state models and mutational scanning of binding energies of the SARS-CoV-2 BA.2 and BA.2.75 receptor binding domain complexes revealed the increased thermodynamic stabilization of the BA.2.75 variant and significant dynamic differences between these Omicron variants. Molecular simulations of the SARS-CoV-2 Omicron spike full-length trimer complexes with the ACE2 receptor complemented atomistic studies and enabled an in-depth analysis of mutational and binding effects on conformational dynamic and functional adaptability of the Omicron variants. Despite considerable structural similarities, Omicron variants BA.2, BA.2.75 and XBB.1 can induce unique conformational dynamic signatures and specific distributions of the conformational states. Using conformational ensembles of the SARS-CoV-2 Omicron spike trimer complexes with ACE2, we conducted a comprehensive cryptic pocket screening to examine the role of Omicron mutations and ACE2 binding on the distribution and functional mechanisms of the emerging allosteric binding sites. This analysis captured all experimentally known allosteric sites and discovered networks of inter-connected and functionally relevant allosteric sites that are governed by variant-sensitive conformational adaptability of the SARS-CoV-2 spike structures. The results detailed how ACE2 binding and Omicron mutations in the BA.2, BA.2.75 and XBB.1 spike complexes modulate the distribution of conserved and druggable allosteric pockets harboring functionally important regions. The results are significant for understanding the functional roles of druggable cryptic pockets that can be used for allostery-mediated therapeutic intervention targeting conformational states of the Omicron variants.

An atomistic study on grain-size and temperature effects on mechanical properties of polycrystal CoCrFeNi high-entropy alloys

The origin of the outstanding mechanical properties of high-entropy alloys (HEAs) is still elusive. In this paper, we have investigated the influence of grain size and temperature on the mechanical properties of polycrystalline CoCrFeNi HEAs via molecular dynamics simulations. The critical grain size for the inverse Hall-Petch effect in CoCrFeNi HEAs is approximately 11.65 nm. During the stage of the positive Hall-Petch effect (where smaller grain sizes lead to higher tensile strength), there is a positive correlation between the tensile strength and dislocation density in CoCrFeNi HEAs. The higher tensile strength at low temperatures in CoCrFeNi HEAs is also attributed to an increase in dislocation density. At low temperatures, the reduced thermal vibrations of atoms slow down the motion of dislocations, leading to an increased storage time of dislocations within the crystal. In the stage of the inverse Hall-Petch effect, due to a significant reduction in grain size, the storage capacity of dislocations within grains decreases. This leads to the accumulation of more dislocations at grain boundaries, forming defects, and consequently causing a decrease in the tensile strength of CoCrFeNi HEAs as the grain size decreases. Our results might be helpful in material design of polycrystal HEAs.

Water flow in a polymeric nanoslit channel with graphene and hexagonal boron nitride wall coatings: An atomistic study

Low flow resistance is essential for the design of nanofluidic platforms. Here, we present a comparative atomic-level study analyzing the fundamentals of water flow enhancement in a polymeric nanochannel due to the implementation of monatomic thick coatings—specifically, graphene and hexagonal boron nitride (hBN). Our results obtained employing large scale non-equilibrium molecular dynamics simulations and continuum models, revealing significant values of slip lengths of ∼29 and ∼6 nm for graphene- and hBN-coated nanochannels, respectively. Equilibrium molecular dynamics simulations, using the Green–Kubo relation, show the significant effect that the partial charges of hBN coating layer have on the water–wall friction. In addition, consistent values of the slip length are obtained from independent sets of equilibrium and non-equilibrium molecular dynamics simulations, confirming that the computed interfacial friction coefficients hold across flow regimes where water molecules no longer occupy the most energetically stable zones at the interface. Hence, the lower interfacial friction observed in the graphene-coated channel leads to a higher water flow enhancement than the one computed in the hBN-coated channel. We also show that the natural undulations of two-dimensional honeycomb-like materials, implemented as wall coatings, remain largely unhindered due to strong interfacial coupling facilitated by π−π stacking between the underlying aromatic polymer substrate and coating monolayers. This is particularly relevant for graphene coatings, which display significant out-of-plane thermal rippling that further enhances water flow. This observation is supported by a stronger atomic-scale vibrational coupling at the water–graphene interface compared to that computed at the water–hBN interface.

Synthesis of hollow bimetallic nanoparticles from Ultrafast Laser Irradiation: An atomistic simulation study

Femtosecond laser irradiation in Au@Ag, Ag@Au core@shell, and Au–Ag Janus-like nanoparticles are investigated using molecular dynamics simulations. Our results show that the morphology of Au@Ag core–shell and Au–Ag Janus-like nanoparticles tend to form hollow-like nanostructures due to the ultrafast energy transfer and the subsequent cooling process. In contrast, our results also shows that Ag@Au nanoparticles do not form a hollow structure due to the high diffusion of Ag atoms and the limited expansion of the Au shell. Besides, successive laser impacts on the Au–Ag Janus-like nanoparticle produce a structure that alternates from hollow to a solid nanoparticle and, at the same time, promotes atomic diffusion, favoring the alloying process of the Ag and Au atoms. In addition, the evolution of the crystalline structure is studied, observing a saturation of the planar defects due to the impossibility of forming a new crystalline phase. The energy variation between the initial and final step, it is not influenced by the presence of the hollow, however it is dominated by the increase of planar defects.

Anticorrosion mechanism of natural acidic amino acids on steel in chloride solution: Experimental, theoretical and machine learning approaches

This paper investigates the corrosion inhibition of steel by two natural acidic amino acids, glutamic acid and aspartic acid, in a 3.5 wt% NaCl solution. The anti-corrosion activity is evaluated using various electrochemical tests, such as potentiodynamic polarization (PDP), electrochemical impedance spectroscopy (EIS), and linear sweep voltammetry (LSV), in addition to quantum chemical calculation and molecular dynamic simulation. Results indicate that the natural compounds act as mixed-type inhibitors with a predominance of anodic inhibition and effectively increase charge transfer resistance and resistance to the solubility of Fe into Fe2+ as inhibitor concentration increases. At a concentration of 0.2 g/L, the inhibition efficiency reaches 57.84% for glutamic acid and 42.99% for aspartic acid. Moreover, the quantum chemistry calculations and molecular dynamics simulations, based on density functional theory (DFT) and Condensed-phase Optimized Molecular Potentials for Atomistic Simulation Studies (COMPASS) force field methods respectively, demonstrate that glutamic acid shows superior corrosion inhibition performance as it has higher binding energy and more stable adsorption on the steel surface than aspartic acid. Additionally, machine learning (ML) methods, including regression analysis and Logic regression, are employed to analyze the data and confirm the better corrosion inhibition performance of glutamate compared to aspartate.

Structures and energies of computed silicon (001) small angle mixed grain boundaries as a function of three macroscopic characters

Small angle grain boundaries comprised of dislocation structures have unique impacts on the performances of crystalline materials. In this atomistic study, we report structure-property correlations of Si (001) small angle mixed grain boundaries (SAMGBs) across three macroscopic GB characters (tilt character, twist character, and an implicit rotation character between them). Firstly, for the computed SAMGB energies spanning the three-dimensional GB character space, a revised Read-Shockley relationship is proposed and fitted, which hints that the energy trends follow the Read-Shockley formalism from the insight of GB decomposition. GB structural transitions from dislocation to amorphous structures are also given as a function of dislocation core radii, allowing the estimation of small angle GB proportion. Then, the proportion, topology and structural signatures of different SAMGB types defined from the ratio between the tilt and twist angles are presented. By extracting the transformation of metastable SAMGB phases, the formation process of these (001) SAMGB structures is characterized as the energetically favorable dislocation glide and reaction, from which the dislocation density function is derived. The relevant results about SAMGB energies and structures are validated and supported by theoretical calculations and experimental observations, respectively.