Computational Dynamics Research Articles

Highly Stable Electronics Based on β-Ga2O3 for Advanced Memory Applications.

Wide-bandgap (WBG) semiconductors are at the forefront of driving innovations in electronic technology, perpetuating Moore's Law and opening up new avenues for electronic devices. Although β-Ga2O3 has attracted extensive research interest in advanced electronics, its high-temperature and high-speed volatile memory applications in harsh environment has been largely overlooked. Herein, a high-performance hexagonal boron nitride (h-BN)/β-Ga2O3 heterostructure junction field-effect transistor (HJFET) is fabricated, exhibiting an off-state current as low as ≈10 fA, a high on/off current ratio of ≈108, a low contact resistance of 5.6 Ω·mm, and an impressive field-effect electron mobility of 156 cm2 （Vs）-1. Notably, the current h-BN/β-Ga2O3 HJFET exhibits outstanding thermal reliability in the ultra-wide temperature range from 223 to 573 K, as well as long-term environmental stability in air, which confirms its inherent capability of operation in harsh environments. Moreover, the h-BN/β-Ga2O3 HJFET demonstrates successful applications for accelerator-in-memory computing fields, including dynamic random-access memory structure and neural network computations. These superior characteristics position β-Ga₂O₃-based electronics as highly promising for applications in extreme environments, with particular relevance to the automotive, aerospace, and sensor sectors.

Silicate liquid immiscibility in the Chang’e 5 lunar mare magmas: constraints on the petrogenesis of lunar granitic rocks

Abstract Silicate liquid immiscibility was a common mechanism during the late-stage evolution of lunar basaltic magmas, which produced co-existing and immiscible Si- and Fe-rich melts. However, the relationship between silicate liquid immiscibility and lunar granitic rocks is debated. In this study, we investigated Si-rich melt inclusions hosted in fayalite fragments from lunar soil returned by the Chang’e 5 mission. These melt inclusions have high SiO2 (76.4 wt.%), Al2O3 (11.1 wt.%), and K2O (5.8 wt.%), and low FeO (2.8 wt.%), TiO2 (0.42 wt.%), and MgO (0.02 wt.%) contents. The texture and chemical composition indicate that these Si-rich melt inclusions formed through late-stage silicate liquid immiscibility of the Chang’e 5 mare basaltic magma. Mass balance considerations show that the unfractionated rare earth element patterns and Eu anomalies of these melt inclusions are similar to those of lunar granitic rocks. Dynamic calculations indicate that the accumulation of Si-rich melt was hindered by the high cooling rate of the Chang’e 5 basaltic magma after eruption. However, in deep-crustal magma chambers, basaltic magma would have cooled slowly and the Si-rich melt generated by late-stage silicate liquid immiscibility would possibly have had enough time to migrate upwards and accumulate to form a granitic melt body of significant size. The results of this study support the possibility that lunar granitic rocks are products of silicate liquid immiscibility.

Tight Binding Simulation of the MgO and Mg(OH)2 Hydration and Carbonation Processes.

Magnesium, the lightest engineering metal, has MgO and Mg(OH)2 as its common corrosion products, which can also be used for CO2 storage due to their chemical reactivity. In this study, we developed a DFTB model with monopole, dipole, and quadrupole electrostatics for magnesium compounds containing oxygen, hydrogen, and carbon and applied it in both static and molecular dynamics (DFTB-MD) calculations of the MgO and Mg(OH)2 hydration and carbonation processes. With our new model, the Electron Localization Function (ELF) and Charge Density Difference (CDD) were computed as part of the electronic structure analysis, providing insights into the electronic mechanism of MgO and Mg(OH)2 hydration and carbonation processes. The geometry for the brucite-water bulk system was analyzed, including the reconstruction of near-surface water molecules which may influence the dissolution, hydration, and carbonation processes. By comparing experimental, DFT, classical MD results and the results from other parameter set, the accuracy of the model was assessed. A strong covalent bond between CO2 and the (001) surface of MgO leads to the formation of a CO3 group, while no such CO3 group forms on the (101̅1) surface of Mg(OH)2. Defect sites, however, are more favorable for the formation of the CO3 group. In contrast, covalent bonds are not found for either surface when water interacted with them. This work provides new insights into the behavior of magnesium compounds interacting with water and carbon dioxide using our model, and it introduces a tool for effectively analyzing chemical electronic structures and bonding mechanisms.

The efficient method of lattice dynamics calculation: Monte Carlo integration with importance sampling.

In this study, we aimed to accelerate the thermal conductivity calculations of crystalline nanostructures using anharmonic lattice dynamics. For this we implemented Monte Carlo integration for relaxation time calculations and achieved a dramatic acceleration of
approximately two orders of magnitude. The relaxation times can be calculated by computing the scattering rates for all phonon combinations; however, in this Monte Carlo integration, we instead calculated the scattering rates of a randomly sampled subset of combinations. Then, we estimated the overall scattering rate. Simple Monte Carlo integration samples the
scattering channels that do not contribute to the total scattering rate, leading to inefficiencies. To address this issue, we implemented an importance sampling method (ISM) for improving sampling efficiency. In this study, we compared the computational speeds of both methods and investigated the differences in accuracy by comparing the results with the exact values obtained
from traditional relaxation time calculations. The comparison showed similarity between both the methods in terms of speed; however, ISM was faster when the error margin was ∼5%. Furthermore, while simple Monte Carlo integration risks significantly worse accuracy as the system size increases, the ISM remains relatively robust and reliable.

Localized Heating Assisted Laser Shock Peening without Coating Enhances Mechanical Properties of Ti6Al4V Alloys

Room-temperature laser shock peening without coating (RT-LSPwoC) is the mainstream method for surface strengthening, yet it induces tensile residual stress on the surface during rapid heating and cooling. Warm LSPwoC, combining the benefits of dynamic strain aging and LSPwoC, exhibits higher performance than RT-LSPwoC. However, overall high-temperature is time- and resource-consuming, and it is prone to causing thermal stress relaxation during processing, making it unsuitable for large-scale applications. In this paper, a novel localized heating assisted LSPwoC (LHA-LSPwoC) method, utilizing a continuous wave laser for local heating, is proposed. Additionally, the deep physics-informed neural network model, embedded with physical formulas, is designed for process optimization. It enables rapid and accurate responses for an extensive number of cases (40 cases with an average deviation below 1%), overcoming the drawbacks of traditional numerical simulations that are time-consuming and difficult to efficiently handle numerous cases. Compared to RT-LSPwoC, LHA-LSPwoC samples have higher dislocation density and higher grain refinement, demonstrating higher hardness and residual stress, particularly superior fatigue performance. The mechanism of LHA-LSPwoC is discussed, and thermally coupled finite element simulations and molecular dynamics calculations are conducted to provide theoretical support. The proposed method is cost-effective and flexible, showing outstanding potential for industrial applications.

Bond Characteristic-Dependent Viscosity Variations in CaF₂-SiO₂-Al₂O₃-MgO Welding Fluxes

Viscosity is critical in welding fluxes as it could affect weldability and alloying element transfer behaviors during submerged arc welding. It is widely accepted that viscosity is intrinsic to bonding structures. However, it is unclear how such structures could modify viscosity in commercial CaF2-SiO2-Al2O3-MgO fluxes. In this study, structure-viscosity correlations have been revealed by employing molecular dynamics calculations coupled with viscosity measurements. The results show that viscosity at 1300°C reaches maximum (1.99 Pa·s) and minimum values (0.10 Pa·s) at the highest SiO2 and MgO levels, respectively. Furthermore, bond stability and distribution could indicate the structural degree of polymerization. Specifically, the proportion of stabilized bridging oxygen and bonded F (Si-F and Al-F) correlates positively with the activation energy of viscous flow. Due to the dilution effect of free F and the depolymerization effect of bonded F, the activation energy of viscous flow in the targeted system (60–130 kJ/mol) is significantly lower than in fluorine-free ones (160–240 kJ/mol). The current investigation establishes a relationship between bond stability and viscous flow activation energy, demonstrating a stronger correlation than considering O-related structural parameters alone.

Integrated approach of coarse-grained molecular dynamics calculations and machine learning for understanding mechanical properties of filler-filled polymer models

Integrated approach of coarse-grained molecular dynamics calculations and machine learning for understanding mechanical properties of filler-filled polymer models

Innovative formaldehyde adsorption with optimized deep eutectic solvents: An experiment and multilevel computational chemistry approach.

Formaldehyde, a hazardous gas that is exposed to everyone every day, has been proven to pose an elevated risk of respiratory problems, allergies, and chronic diseases. Adsorption technologies have proven to be a straightforward and labor-saving method to reduce indoor formaldehyde levels. Currently, extensive research has been conducted utilizing Deep Eutectic Solvents (DES) as adsorbents for harmful gases, yet the adsorption and conversion mechanisms for formaldehyde remain unclear. In this study, we highlighted the adsorption and transformation mechanisms of formaldehyde with DES employing quantum chemical and molecular dynamics calculations. Initially, thermodynamic software (CosmoTherm) was employed to calculate the logarithmic activity coefficients (LAC) of formaldehyde and determine the solid-liquid equilibrium (SLE) for 416 combinations of DES. On the basis of the eutectic point and LAC of DES, potential formaldehyde adsorbents were screened. In the second step, the DES screened out has a good formaldehyde adsorption capacity through the experiment. Finally, the reactive sites, reaction pathways, van der Waals interactions, and hydrogen bonds of DES of L-cysteine/diethanolamine (CYS-DEA) and formaldehyde were studied through a theoretical approach. This study comprehensively elucidates the screening of formaldehyde adsorbents, experimental adsorption, and adsorption mechanisms. Significantly shortens the development cycle of DES as formaldehyde adsorbents.

Eccentric Wear Mechanism and Centralizer Layout Design in 3D Curved Wellbores

In deep oil and gas wells, sucker rod strings (SRS) frequently experience breakage and eccentric wear problems. To address this engineering challenge, this study establishes a new coupled three-dimensional (3D) mechanical-mathematical model for sucker rod strings in 3D curved wellbores. The model comprehensively considers well trajectory, rod string structure, and external excitation, analysing the influences of elastic force, inertial force, and friction force on the sucker rod micro-elements. The formulated differential equations are discretised using the central difference method to obtain the configuration of each point on SRS and the 3D distribution of stress and strain, thereby determining the eccentric wear points between the rod and tube. A numerical solution program was developed and successfully applied in the Daqing oilfield. Results from two case studies demonstrate significant improvements: for A1# well, the system efficiency increased from 16% to 20%, while for A2# well, the pump efficiency improved from 39.8% to 58.9% and system efficiency from 33.4% to 35%. The model overcomes previous limitations by considering rod torque, 3D curved tubing spatial coordinates, tubing non-anchoring effects, and forced buckling influence, providing a theoretical basis for dynamic calculations of sucker rod pumping systems in 3D curved wells.

Machine learning-accelerated molecular dynamics calculations for investigating the thermal modulation by ferroelectric domain wall in KTN single crystals

Machine learning-accelerated molecular dynamics calculations for investigating the thermal modulation by ferroelectric domain wall in KTN single crystals

In Silico Discovery of SARS-CoV-2 Main Protease Inhibitors Using Docking, Molecular Dynamics, and Fragment Molecular Orbital Calculations.

The 3C-like protease of severe acute respiratory syndrome coronavirus 2, known as the main protease (Mpro), is an attractive drug target for the treatment of coronavirus disease 2019. This study reports the discovery of novel Mpro inhibitors using several in silico techniques, including docking, molecular dynamics (MD), and fragment molecular orbital (FMO) calculations. We performed docking calculations on 5950 compounds with bioactivity, and 12 compounds were selected. An enzymatic assay was conducted, revealing that BP-1-102 exhibits significant Mpro inhibitory activity with an IC50 of 11.1 μM. The identification of seed compounds from the experiments on a few compounds demonstrates the effectiveness of our docking calculations. Furthermore, the detailed analyses using MD and FMO calculations suggested an interaction mechanism in which the hydroxyl group of BP-1-102 forms a hydrogen bond with E166 of Mpro. The Mpro inhibitory activity of SH-4-54, a derivative without the aforementioned hydroxyl group, was investigated and observed to be significantly reduced, with an IC50 of 81.5 μM. This result strongly supports the suggested interaction mechanism.

A physical optics formulation of Bloch waves and its application to 4D STEM, 3D ED and inelastic scattering simulations.

Bloch waves are often used in dynamical diffraction calculations, such as simulating electron diffraction intensities for crystal structure refinement. However, this approach relies on matrix diagonalization and is therefore computationally expensive for large unit cell crystals. Here Bloch wave theory is re-formulated using the physical optics concepts underpinning the multislice method. In particular, the multislice phase grating and propagator functions are expressed in matrix form using elements of the Bloch wave structure matrix. The specimen is divided into thin slices, and the evolution of the electron wavefunction through the specimen calculated using the Bloch phase grating and propagator matrices. By decoupling specimen scattering from free space propagation of the electron beam, many computationally demanding simulations, such as 4D STEM imaging modes, 3D ED precession and rotation electron diffraction, phonon and plasmon inelastic scattering, are considerably simplified. The computational cost scales as {\cal O}({N^2} ) per slice, compared with {\cal O}({N^3} ) for a standard Bloch wave calculation, where N is the number of diffracted beams. For perfect crystals the performance can at times be better than multislice, since only the important Bragg reflections in the otherwise sparse diffraction plane are calculated. The physical optics formulation of Bloch waves is therefore an important step towards more routine dynamical diffraction simulation of large data sets.

Electronically Nonadiabatic Quenching of Excited States of O2 by Collisions with O Atoms.

The kinetics of electronically inelastic quenching of O2(a1Δg) and O2(b1Σg+) by collisions with O(3P) have been investigated using mixed quantum-classical trajectories governed by adiabatic potential energy surfaces and state couplings generated from a recently developed diabatic potential energy matrix (DPEM) for the 14 lowest-energy 3A' states of O3. Using the coherent switching with decay of mixing (CSDM) method, dynamics calculations were performed both with 14 coupled electronic states and with 8 coupled electronical states, and similar results were obtained. The calculated thermal quenching rate coefficients are generally small, but they increase with temperature. The positive temperature dependence is attributed to high-energy locally avoided crossings that can only be easily accessed by high collision energies. We find that, depending on the temperature, 86-97% of the b state quenches are into the a state with the remainder into the ground electronic state of O2. The calculated rate coefficients for quenching of O2(b1Σg+) and O2(a1Δg) by O(3P), coupled with the assumption that electronically nonadiabatic probabilities for collisions on the 3A' surfaces are similar to those on 3A″ surfaces, are compared with the available experimental results.

Virtual screening of potential inhibitors of the ATPase site in Acinetobacter baumannii DNA Gyrase.

Bacterial resistance is a global public health problem because of the ineffectiveness of conventional antibiotics against super pathogens. To counter this situation, the search for or design of new molecules is essential to inhibit the key proteins involved in several stages of bacterial infection. One of these key proteins is DNA gyrase, which is responsible for packaging and unfolding of DNA chains during replication. Virtual screening calculations of 583,900 molecules against the ATPase site of DNA gyrase (PDB ID 7PQM) resulted in three promising molecules (Z927783420, Z4422201766, and Z2440107042) with significant binding modes at the active site, according to molecular docking studies. Additionally, they exhibited lower toxicological profiles than the previously reported 80S inhibitors. Molecular dynamics calculations revealed crucial interactions responsible for the inhibition process, with residues ASP87, GLU94, and ASN60 belonging to the ATPase site. On the other hand, the binding energy calculated using the MM/GBSA protocol highlighted Z2440107042 as the most promising inhibitor, with the best binding energy (-74.77kcal/mol), suggesting that this molecule is a strong candidate for further biological studies.

Challenging the ideal strength limit in single-crystalline gold nanoflakes through phase engineering

Materials usually fracture before reaching their ideal strength limits. Meanwhile, materials with high strength generally have poor ductility, and vice versa. For example, gold with the conventional face-centered cubic (FCC) phase is highly ductile while the yield strength (~102 MPa) is significantly lower than its ideal theoretical limit. Here, through phase engineering, we show that defect-free single-crystalline gold nanoflakes with the hexagonal close-packed (HCP) phase can exhibit a strength of 6.0 GPa, which is beyond the ideal theoretical limit of the conventional FCC counterpart. The lattice structure is thickness-dependent and the FCC-HCP phase transformation happens in the range of 11–13 nm. Suspended-nanoindentations based on atomic force microscopy (AFM) show that the Young’s modulus and tensile strength are also thickness-and phase- dependent. The maximum strength is reached in HCP nanoflakes thinner than 10 nm. First-principles and molecular dynamics (MD) calculations demonstrate that the mechanical properties arise from the unconventional HCP structure as well as the strong surface effect. Our study provides valuable insights into the fabrication of nanometals with extraordinary mechanical properties through phase engineering.

Ultrafast Dissociation Dynamics of the Sensitive Explosive Ethylene Glycol Dinitrate.

Ethylene glycol dinitrate (EGDN) is a nitrate ester explosive widely used in military ordnance and missile systems. This study investigates the decomposition dynamics of the EGDN cation using a comprehensive approach that combines femtosecond time-resolved mass spectrometry (FTRMS) experiments with ab initio electronic structure and molecular dynamics computations. We identify three distinct dissociation time scales for the metastable EGDN cation of approximately 40-60 fs, 340-450 fs, and >2 ps. The observed dissociation time scales are rationalized by electronic and geometric relaxation of multiple EGDN conformers. These insights are crucial for advancing knowledge of the initial molecular decomposition processes that are central to the detonation physics of nitrate esters, which can lead to improving safety protocols and optimizing the performance of nitrate ester explosives in various applications.

Computational Explorations of Th4+ First Hydrolysis Reaction Constants: Insights from Ab Initio Molecular Dynamics and Density Functional Theory Calculations.

The fundamental hydrolysis behavior of tetravalent actinide cations (An4+) with a high charge is crucial for understanding their solution chemistry, particularly in nuclear fuel reprocessing and environmental behavior. Using Th4+ as a reference of the An4+ series, this work employed both the periodic model and the cluster model to calculate the first hydrolysis reaction constant (pKa1) of the Th4+ aqua ion and conducted a detailed evaluation of these approaches. In the periodic model, ab initio molecular dynamics (AIMD) simulations of Th4+ in the explicit solvation environment are conducted, using metadynamics and constrained molecular dynamics to calculate pKa1 values. Metadynamics simulations with sufficient sampling yielded a value of 5.02, aligning with the experimental values (4.12-4.97). Moreover, AIMD results reveal further Grotthuss-type proton transfers and changes in the solvent structures, which are important for accurately modeling the hydrolysis process. In the cluster model, density functional theory calculations are performed on isolated hydrate clusters to obtain pKa1 values, describing solvation effects through the cluster-continuum model. Based on insights from the periodic models, particularly regarding further proton transfer, the cluster model was modified and tested using different functionals and similar cations (La3+and Ac3+). The pKa1 values obtained in the cluster model also show good agreement with the experimental values. The current computational approaches provide a comprehensive understanding of Th4+ hydrolysis and a reference framework for studying the hydrolysis of other lanthanide and actinide ions.

Development of a novel laboratory approach for evaluating the adhesion strength of biofilms to human dentine.

Biofilms may show varying adherence strengths to dentine. This study quantified the shear force required for the detachment of multispecies biofilm from the dentine using fluid dynamic gauging (FDG) and computation fluid dynamics (CFD). To date this force has not been quantified. Multispecies biofilms were grown over 3, 7 and 14 days on 2 mm thick dentine sections of human molars (n = 8 per group). The FDG technique with different suction flow rates (100%, 80% and 40%) was used to assess biofilm removal. At maximum suction (100%), the flow rate was 500 mL/min. Digital images of each stained dentine sample were captured (10× magnification) before and after subjecting the samples to the various suction flow rates. The change in colour saturation versus control (△E) value was determined to assess removal of biofilm using digital softwares (Image J© and Colormine©). The imposed shear forces were then estimated using CFD and correlated with the △E values. FDG and CFD analysis showed that complete removal of biofilm by using water as the gauging liquid was not possible across any of the experimental groups. Three-day biofilms required significantly lower shear forces for removal than 7-day or 14-day biofilms. The maximum shear forces were seen in the 14-day biofilm group at all flow rates tested. When assessing for residual biofilm on the dentine, the △E value showed residual biofilms of approximately 40% at all time periods at a 100% flowrate. Complete removal of multispecies biofilm was not possible in any experimental group. This study for the first-time records forces needed to remove polymicrobial biofilms form the surface of a dentine sample. Within the limits of this study, mature biofilms require greater shear forces for removal. This is important when planning protocols for biofilm removal.

Accurate machine learning of rate coefficients for state-to-state transitions in molecular collisions.

We present an algorithm that combines quantum scattering calculations with probabilistic machine-learning models to predict quantum dynamics rate coefficients for a large number of state-to-state transitions in molecule-molecule collisions much faster than with direct solutions of the Schrödinger equation. By utilizing the predictive power of Gaussian process regression with kernels, optimized to make accurate predictions outside of the input parameter space, the present strategy reduces the computational cost by about 75%, with an accuracy within 5%. Our method uses temperature dependences of rate coefficients for transitions from the isolated states of initial rotational angular momentum j, determined via explicit calculations, to predict the temperature dependences of rate coefficients for other values of j. The approach, demonstrated here for rovibrational transitions of SiO due to thermal collisions with H2, uses different prediction models and is thus adaptive to various time and accuracy requirements. The procedure outlined in this work can be used to extend multiple inelastic molecular collision databases without exponentially large computational resources required for conventional rigorous quantum dynamics calculations.

Stability of Proton Superoxide and its Superionic Transition Under High Pressure.

Under extreme conditions, condensed matters are subject to undergo a phase transition and there have been many attempts to find another form of hydroxide stabilized over H2O. Here, using Density Functional Theory (DFT)-based crystal structure prediction including zero-point energy, it is that proton superoxide (HO2), the lightest superoxide, can be stabilized energetically at high pressure and temperature conditions. HO2 is metallic at high pressure, which originates from the 𝜋* orbitals overlap between adjacent superoxide anions (O2 -). By lowering pressure, it undergoes a metal-to-insulator transition similar to LiO2. Ab initio molecular dynamics (AIMD) calculations reveal that HO2 becomes superionic with high electrical conductivity. The possibility of creating hydrogen-mixed superoxide at lower pressure using a (Lix,H1-x)O2 hypothetical structure is also proposed. This discovery bridges gaps in superoxide and superionicity, guiding the design of various H-O compounds under high pressure.