Density Functional Molecular Dynamics Research Articles

Nanoporous Ti3C2O2 monolayer towards high permeance and selectivity for CO2/N2 separation: CO2-MXene interaction tuning

MXene, as a new gas separation membrane, has good stability and suitable pore topological structures to mitigate the greenhouse effect caused by excessive CO2 emission. However, the large quadrupole and polarizability of CO2 make it a strong interaction with MXene, thus leading to a strong solubility and weak diffusivity of CO2. Here, we design nanoporous Ti3C2O2 monolayers (YmXn) with exposed C atoms that could tune CO2-Ti3C2O2 interaction so as to improve gas separation performance by density functional theory and molecular dynamics simulation. The scope of “Cut-off” size is obtained by analyzing the gas separation state from un-permeation to permeation. Results reveal that nanoporous Ti3C2O2 membranes achieve both outstanding CO2 selectivity and permeance. The best-performance Y3X3-Ti possesses CO2 permeance of 1.01 × 10-4 and 2.56 × 10-5 mol s−1 m−2 Pa−1 for equimolar gas mixtures and flue gases, respectively, and both the CO2/N2 selectivity reach 100 %. The gas separation mechanism is dominated by diffusion selectivity rather than solution selectivity in nanoporous Ti3C2O2. The dynamic processes of gas permeation, including the center of mass, mean square displacement, and radial distribution function of the gases, are precisely investigated. The electrostatic repulsion between the C atoms in the channel of the membrane and CO2 follows the sequence Y3X3-C > Y2X4 > Y3X3-Ti, which is the key to regulating gas diffusion. Results of this work highlight that tuning gas-membrane interaction and designing “Cut-off” size are effective strategies to achieve excellent CO2 separation performance, and shed new light on the intrinsic mechanism in high-performance gas separation membranes.

Experimental and theoretical investigation of 1-Hexyl-3-methylimidazolium iodide as a corrosion inhibitor for mild steel in HCl environment

This study employed 1-Hexyl-3-methylimidazolium iodide to mitigate the corrosion of Q235 steel in a hydrochloric acid environment. The evaluation of corrosion inhibition effectiveness was comprehensively characterized by combining electrochemical experiments with surface morphology observation. The experimental results demonstrated the capability of the ionic liquid in establishing a film layer on the surface of Q235 steel, which effectively hindered the charge transfer process. Notably, the corrosion inhibition efficiency attained a value of 92.3% at a concentration of 1 mM corrosion inhibitor. Moreover, the process of the corrosion inhibitor adhering to the steel surface aligns with the Langmuir isotherm, demonstrating physicochemical adsorption behavior. The density functional theory (DFT) and molecular dynamics (MD) simulation were utilized for further exploration of the corrosion inhibition mechanism, and the results indicate the ionic liquid can be adsorbed onto the (110) surface of Fe in parallel through N atoms on the imidazole ring.

Experimental and Theoretical Insights into Interfacial Properties of 2D Materials for Selective Water Transport Membranes: A Critical Review.

Interfacial properties, such as wettability and friction, play critical roles in nanofluidics and desalination. Understanding the interfacial properties of two-dimensional (2D) materials is crucial in these applications due to the close interaction between liquids and the solid surface. The most important interfacial properties of a solid surface include the water contact angle, which quantifies the extent of interactions between the surface and water, and the water slip length, which determines how much faster water can flow on the surface beyond the predictions of continuum fluid mechanics. This Review seeks to elucidate the mechanism that governs the interfacial properties of diverse 2D materials, including transition metal dichalcogenides (e.g., MoS2), graphene, and hexagonal boron nitride (hBN). Our work consolidates existing experimental and computational insights into 2D material synthesis and modeling and explores their interfacial properties for desalination. We investigated the capabilities of density functional theory and molecular dynamics simulations in analyzing the interfacial properties of 2D materials. Specifically, we highlight how MD simulations have revolutionized our understanding of these properties, paving the way for their effective application in desalination. This Review of the synthesis and interfacial properties of 2D materials unlocks opportunities for further advancement and optimization in desalination.

Mechanical behavior of Ni/Ti bilayer-based shape memory alloys: Endorsement via atomistic simulations

To gain a structural and thermodynamic understanding along with the interpretation of atomic diffusion in a Ni/Ti bilayer, detailed first-principles simulations using density functional theory (DFT) and molecular dynamics (MD) simulations have been carried out. The interface energies and electronic structure of the Ni/Ti bilayer have been calculated using DFT. The MD simulations of interface atomic diffusion in the Ni/Ti bilayer were performed at 773 K for different annealing times to investigate the formation of Ni–Ti alloy. The simulated results indicate that Ni atoms predominantly diffuse into the Ti side. The radial distribution functions (RDFs) have been plotted to understand the nature of bonding that exists between the Ni and Ti atoms in the bilayer. The shape of the RDFs reveals information about the extent to which Ni and Ti atoms mix together. Classical MD simulations have been used to simulate the deformation behavior of the material under tension and to investigate the effects of annealing time on the mechanical properties of the materials.

Mechanistic study of direct coupling of CO2 and C2H4 over atomically dispersed metal at graphene edges

Direct coupling of CO2 and ethylene (hereinafter DCCE) to acrylic acid is valuable for valorizing CO2 to manufacture acrylate-derived products. However, previous studies in DCCE have been limited on molecular catalysts with challenges in improving catalytic performance. In this work, we employed density functional theory calculations and ab initio molecular dynamics simulations to investigate the heterogeneous catalysis of DCCE over atomically dispersed metal centers at nitrogen-doped zigzag edge of graphene. Based on competitive adsorption and structural stability, Mo, Cr, V, Ru, and Ni active sites are chosen to explore the reaction kinetics. We find that the activation barriers are determined by the charge redistribution at transition states, which explains the trend of activity for the C-C coupling and the hydrogen transfer, two key steps in DCCE. Furthermore, we show that the intramolecular hydrogen transfer (rate-limiting step) is hindered due to the lack of local coordinate at the active sites. We thus propose to use co-adsorbed water as a “proton-exchanger” following a water-assisted route, and show that the activation barriers are reduced over all metal centers. Particularly, water promotes the hydrogen transfer over metals with strong CO2-ethylene co-activation and facile C-C coupling kinetics, which could be considered promising for DCCE. In both mechanisms, the stability of metallactone intermediate can be used to predict the catalytic activity. It is anticipated that the insights from this work can provide guidelines for mimicking well-defined multifunctional active sites in molecular catalysts to design heterogeneous catalysts for such C-C coupling, which advances catalytic utilization of CO2.

Atoms as words: A novel approach to deciphering material properties using NLP-inspired machine learning on crystallographic information files (CIFs)

In condensed matter physics and materials science, predicting material properties necessitates understanding intricate many-body interactions. Conventional methods such as density functional theory and molecular dynamics often resort to simplifying approximations and are computationally expensive. Meanwhile, recent machine learning methods use handcrafted descriptors for material representation, which sometimes neglect vital crystallographic information and are often limited to single property prediction or a sub-class of crystal structures. In this study, we pioneer an unsupervised strategy, drawing inspiration from natural language processing to harness the underutilized potential of Crystallographic Information Files (CIFs). We conceptualize atoms and atomic positions within a crystallographic information file similarly to words in textual content. Using a Word2Vec-inspired technique, we produce atomic embeddings that capture intricate atomic relationships. Our model, CIFSemantics, trained on the extensive material project dataset, adeptly predicts 15 distinct material properties from the CIFs. Its performance rivals that of specialized models, marking a significant step forward in material property predictions.

Computational analysis of anionic dyes adsorption on the kaolinite (001) surface: Combination of quantum chemical calculations and molecular simulation methods

Clay minerals are increasingly used to remove dyes from wastewater. In recent times, computational simulation methods have become indispensable for investigating the adsorption mechanisms of dyes on clay surfaces at the molecular level. This study investigates the adsorption features of two acid dyes, namely acid blue 25 (AB25) and acid red 88 (AR88), on the (001) surface of kaolinite in an aqueous medium using density functional theory (DFT), Monte Carlo (MC), and molecular dynamics (MD) simulations. Quantum chemical parameters (QCPs) show that the AB25 molecule exhibits higher reactivity compared to the AR88 molecule. As well, analysis of the sigma profile reveals a moderate polarity of the two dye molecules studied in comparison with the water molecule. The low-energy adsorption configuration of AB25 and AR88 molecules show that each molecule is oriented parallel to the (001) surface of kaolinite over short distances. The adsorption energies indicate that the kaolinite (001) surface has high affinity towards AB25 in comparison with the AR88 molecule (Eads(AB25) = -926.01 Kcal.mol−1; Eads(AR88) = -742.08 Kcal.mol−1), which was supported by analysis of the self-diffusion coefficient (SDC) values (SDCAB25 = 7.79 × 10-10 m2.s−1; SDCAR88 = 1.4 × 10-9 m2.s−1). Additionally, calculation of the radial distribution function of the oxygen and nitrogen atoms of AB25 and AR88 molecules show the contribution of these atoms in the chemical interactions that take place with the (001) surface of kaolinite. The adsorption mechanism of the investigated dye molecules may be influenced by both donor–acceptor and van der Waals interactions. The theoretical results from this study could be useful for better understanding the adsorption mechanisms of other acid dyes on clay minerals.

Electrical conductivity of hydrogen plasmas: Low-density benchmarks and virial expansion including e–e collisions

An improved virial expansion for the low-density limit of the electrical conductivity σ(T,n) of hydrogen as the simplest ionic plasma is presented. Quantum statistical methods provide exact values for the lowest virial coefficients, which serve as a benchmark for analytical approaches to electrical conductivity as well as for numerical results from density functional theory-based molecular dynamics simulations (DFT-MD) or path-integral Monte Carlo simulations. The correction factor introduced by Reinholz et al. [Phys. Rev. E 91, 043105 (2015)] is applied to describe the inclusion of electron–electron collisions in DFT-based calculations of transport coefficients. As a benchmark, the first virial coefficient is correctly described with this approach. The value of the second virial coefficient is discussed, and questions about its value according to DFT-MD simulations are addressed.

High Breakthrough Pressure in Hydrogels Enabled Ultrastable Treatment of Hypersaline Wastewaters.

Surface effects of low-surface-tension contaminants accumulating at the evaporation surface easily induce wetting in membrane distillation, especially in hypersaline scenarios. Herein, we propose a novel strategy to eliminate the surface effect and redistribute contaminants at the evaporation interface simply by incorporating a layer of hydrogel. The as-fabricated composite membrane exhibits remarkable stability, even when exposed to solution with salt concentration of 5 M and surfactant concentration of 8 mM. Breakthrough pressure of the membrane reaches 20 bar in the presence of surfactants, surpassing commercial hydrophobic membranes by one to two magnitudes. Density functional theory and molecular dynamics simulations reveal the important role of the hydrogel-surfactant interaction in suppressing the surface effect. As a proof of concept, we demonstrate the membrane in stably processing synthetic wastewater containing 144 mg L-1 surfactants, 1 g L-1 mineral oils, and 192 g L-1 NaCl, showing its potential in addressing challenges of hypersaline water treatment.

Diving deep into the superior lubrication efficiency: A dynamic approach incorporating covalent organic polymer as strengthening booster in paraffin oil through a holistic blend of experimental and computational approaches

This research addresses the paramount importance of enhancing surface protection and minimizing friction in mechanical systems through the novel design of covalent organic polymer additive (COPA). COPA-1 and COPA-2 were intricately designed to enhance surface protection and minimize wear. Tribological analysis revealed that the addition of an optimized concentration of COPA-1 (25 ppm) to base oil significantly reduced friction (∼60.49% decrease) and wear (∼79.23% decrease) while increasing load-bearing capacity to 588 N. Rheological analysis confirmed excellent shear stability and desirable viscosity behavior. Furthermore, computational tools like density functional theory and molecular dynamics simulations provided valuable insights into the adsorption mechanisms and tribological performance. This integration of experimental and computational insights highlights the transformative potential of COPA in revolutionizing lubrication technology.

Computational study and ion diffusion analyses of native defects and indium alloying in β-Ga2O3 structures

Wide band gap semiconductors like gallium oxide are promising materials for high-power optoelectronic device applications. We show here a combined density functional theory and molecular dynamics study of diffusion pathways for different defects in β-Ga2O3. Molecular dynamics simulations result in a smaller equilibrium volume compared to density functional theory, but the overall lattice remains relatively unchanged even with the inclusion of defects, outside of the local distortions that occur to accommodate the presence of a defect. Slight thermal expansion occurs with elevated temperature and a combination of electron localization function and Bader charge analysis reveals that the oxygen interstitial is the most mobile defect as temperature is increased. However, interstitial cations may diffuse at elevated temperature due to a relatively small amount of charge transfer between the defect and lattice. The mobile oxygen defects are shown to increase the mobility of oxygen ions from the lattice, which can be beneficial for electrochemical applications when controlled through annealing processes.

SMATool: Strength of materials analysis toolkit

The study of the strength of materials is a cornerstone in material science and engineering, playing a critical role in shaping the progress and application of materials in diverse industrial sectors. The strength of a material is meticulously examined to understand the behavior of the material under different stress conditions and environments, thereby guiding material selection and structural design. Herein, we introduce the SMATool, a computational toolkit for the efficient calculation and analysis of material strength at both zero and finite temperatures for 3D, 2D, 1D, and tubular 2D-based nanostructures and nanotubes, as well as 1D nanoribbons. The toolkit is capable of calculating tensile, shear, ultimate, yield, and indentation (Vickers' hardness) strengths in various dimensions, as well as the energy storage capacity. We conducted several calculations both at zero and finite temperatures to validate the accuracy and reliability of the developed software. The results show that the SMATool package provides accurate predictions that align with existing data on material strength. SMATool integrates seamlessly with widely used electronic structure codes like VASP and Quantum Espresso, providing a user-friendly interface catering to academic researchers and industry professionals. SMATool is useful for either the exploration of the strength of materials or high-throughput new material design. SMATool is open-source and available on GitHub at SMATool@github and at Zenodo at 10.5281/zenodo.10780514. Program summaryProgram Title: SMAToolCPC Library link to program files:https://doi.org/10.17632/fnkzfsg7t7.1Licensing provisions: GNU General Public License, version 3Programming language: Python 3Nature of problem: Developing a comprehensive framework to accurately determine the strength of materials is crucial in various engineering and scientific disciplines. This involves developing a robust and efficient computational toolkit to predict the strength of a material under different loading conditions, including tension, compression, shear, and indentation.Solution method:SMATool effectively addresses the challenge of accurately simulating the mechanical properties of materials by leveraging advances in ab initio methods, including density functional theory and molecular dynamics within the atomic simulation environment. The SMATool toolkit can efficiently compute various material strengths, such as tensile, shear, ultimate, yield, and indentation (Vickers' hardness) strengths as well as the corresponding energy storage capacity of the material. It is adept at handling a variety of material dimensions, ranging from 1D nanotubes and nanoribbons to 2D and 3D structures, at both zero and finite temperatures. SMATool currently integrates VASP and Quantum Espresso as the stress calculator and is easily adaptable to use other electronic structure codes.Additional comments including restrictions and unusual features:SMATool offers serial and parallel execution. Depending on the system size, the nature of the calculations (zero or finite temperature), and the computing architecture, the computing time can vary from ∼5 minutes to as high as 18 hours.

Moiré Pattern Controlled Phonon Polarizer Based on Twisted Graphene.

Twisted van der Waals materials featuring Moiré patterns present new design possibilities and demonstrate unconventional behaviors in electrical, optical, spintronic, and superconducting properties. However, experimental exploration of thermal transport across Moiré patterns has not been as extensive, despite its critical role in nanoelectronics, thermal management, and energy technologies. Here, thefirst experimental study is conducted on thermal transport across twisted graphene, demonstrating a phonon polarizer concept from the rotational misalignment between stacked layers. The direct thermal and acoustic measurements,structural characterizations, and atomistic modeling, reveal a modulation up to 631% in thermal conductance with various Moiré angles, while maintaining a high acoustic transmission. By comparing experiments with density functional theory and molecular dynamics simulations, mode-dependent phonon transmissions are quantified based on the angle alignment of graphene band structures and attributed to the coupling among flexural phonon modes. The agreement confirms the dominant tuning mechanisms in adjusting phonon transmission from high-frequency thermal modes while having negligible effects on low-frequency acoustic modes near Brillouin zone center. This study offers crucial insights into the fundamental thermal transport in Moiré structures, opening avenues for the invention of quantum thermal devices and new design methodologies based on manipulations of vibrational band structures and phonon spectra.

Effects of TiC addition on the interface stability, microstructure, and mechanical properties of IN718 fabricated by laser direct metal deposition: A combined experimental, DFT and MD study

In this study, we reveal the impact of the addition of TiC in the IN718 superalloys at both atomic and micron scales through density functional theory (DFT), molecular dynamics (MD), and experimental analysis. From the micro scales, the addition of TiC can effectively mitigate the segregation behavior of Nb and Mo atoms, promote heterogeneous nucleation, reduce grain size, and thus improve mechanical properties. From the atomic scales, the effect of alloying elements (Fe, Cr, Mo, Nb, Co) on the stability of the TiC/γ-Ni interface was investigated through first principles. Co-doping interface was more stable than other interfaces by MD calculations, followed by Cr and Fe-doping models. The heat of segregation results inferred that TiC can effectively mitigate the segregation behavior of Nb and Mo atoms in the TiC/γ-Ni interface, it is mutually verified with the experimental results. Furthermore, the interface energy values theoretically illustrated that TiC particles could promote the heterogeneous nucleation of γ-Ni, this behavior of TiC particles was verified by experiment results. This investigation results provide reference information in the study of ceramic particle reinforced alloys at atomic and micron scales.

Review of Recent Computational Research on the Adsorption of PFASs with a Variety of Substrates.

The widespread use and impervious nature of per- and polyfluorinated alkyl substances (PFASs) is leading to potentially harmful exposure in numerous environments. One avenue to explore remediation of PFAS-contaminated environments involves investigating how well PFASs adsorb onto various substrates. In the current review, we focus on summarizing recent computational research, largely involving density functional theory (DFT) and molecular dynamics (MD), into the adsorption and interaction of PFASs with a variety of substrates with an aim to provide insight and inspire further research that may lead to solutions to this critical problem that impacts the environment and human health.

Towards atomistic modelling of solid Pb-O formation and dissolution in liquid lead coolant: Interatomic potential development

Microscopic description of solid Pb-O formation and dissolution in liquid lead coolant is important for the modelling of fast neutron reactors. For this purpose, in this work we develop interatomic potential models for lead melt with dissolved oxygen. Potentials fitting is based on ab initio density functional theory (DFT) calculations and quantum molecular dynamics. Two different potential models are trained on the DFT data using the force-matching method: a computationally cheap embedded atom method (EAM) potential and a computationally expensive machine-learned moment tensor potential (MTP) that allows reproducing DFT data very accurately. The potentials are further validated to reproduce the properties of lead melt and the coordination of oxygen atoms in molten lead. The diffusion coefficient for oxygen in molten lead is calculated and compared with the available experimental data. We analyse how these interatomic potential models describe the crystal structure of the solid lead oxide to consider PbO nucleation and dissolution in molten lead. We extensively discuss the arising problems with the description of long-range electrostatic interactions. The possibility of matching the experimental data on the oxygen solubility limit by tuning the EAM potential is shown.

Low‐coordination Nanocrystalline Copper‐based Catalysts through Theory‐guided Electrochemical Restructuring for Selective CO2 Reduction to Ethylene

AbstractRevealing the dynamic reconstruction process and tailoring advanced copper (Cu) catalysts is of paramount significance for promoting the conversion of CO2 into ethylene (C2H4), paving the way for carbon neutralization and facilitating renewable energy storage. In this study, we initially employed density functional theory (DFT) and molecular dynamics (MD) simulations to elucidate the restructuring behavior of a catalyst under electrochemical conditions and delineated its restructuring patterns. Leveraging insights into this restructuring behavior, we devised an efficient, low‐coordination copper‐based catalyst. The resulting synthesized catalyst demonstrated an impressive Faradaic efficiency (FE) exceeding 70 % for ethylene generation at a current density of 800 mA cm−2. Furthermore, it showed robust stability, maintaining consistent performance for 230 hours at a cell voltage of 3.5 V in a full‐cell system. Our research not only deepens the understanding of the active sites involved in designing efficient carbon dioxide reduction reaction (CO2RR) catalysts but also advances CO2 electrolysis technologies for industrial application.

Self-formation of the protective film on mild steel surface in hydrochloric acid medium containing Papaya resin extract

Plant extracts have been considered to be an effective corrosion inhibitor due to their high inhibition performance, huge amount, regeneration, and nature, as well as biological sources. However, several steps in the plant extract processes and extracted solvents are still questionable. Therefore, Papaya resin - extract (PRE) was recommended, produced, and characterized as a mixed-type inhibitor for corrosion of mild steel in 0.1 M hydrochloric acid medium. The results indicated that the 2000 ppm of PRE inhibitor has significant effects on the inhibition efficiency, reaching a remarkable value of 98.08% for mild steel in the investigated solution. The potentiodynamic polarization results showed that the PRE inhibitor acts as a mixed-type inhibitor with a dominant anodic inhibitor for mild steel. Moreover, electrochemical impedance spectroscopy and linear polarization resistance results demonstrated that PRE molecules can form protective film, and increase charge transfer and polarization resistances, suggesting the improved steel corrosion resistances. The scanning electron microscope results indicated less occurrence of corrosion on the steel surface exposed to the inhibitor system. Meanwhile, X-ray photoelectron spectroscopy results demonstrated that PRE’s molecules were absorbed and created reactions with iron products to form a protective film on the steel surface. Furthermore, density functional theory (DFT) and molecular dynamics simulation were used to calculate, suggesting that the conjugation effect of two double bonds in PRE’s molecules creates an electron-withdrawing effect on the reactive space around. Moreover, the results revealed the good adhesion and thermal stability of the absorbent protective layer, indicating an agreement with experimental characteristics. Therefore, this result suggests a contemporary design for developing the self-corrosion inhibitor based on natural products with less steps in the synthetic process.

Low-coordination Nanocrystalline Copper-based Catalysts through Theory-guided Electrochemical Restructuring for Selective CO2 Reduction to Ethylene.

Revealing the dynamic reconstruction process and tailoring advanced copper (Cu) catalysts is of paramount significance for promoting the conversion of CO2 into ethylene (C2H4), paving the way for carbon neutralization and facilitating renewable energy storage. In this study, we initially employed density functional theory (DFT) and molecular dynamics (MD) simulations to elucidate the restructuring behavior of a catalyst under electrochemical conditions and delineated its restructuring patterns. Leveraging insights into this restructuring behavior, we devised an efficient, low-coordination copper-based catalyst. The resulting synthesized catalyst demonstrated an impressive Faradaic efficiency (FE) exceeding 70 % for ethylene generation at a current density of 800 mA cm-2. Furthermore, it showed robust stability, maintaining consistent performance for 230 hours at a cell voltage of 3.5 V in a full-cell system. Our research not only deepens the understanding of the active sites involved in designing efficient carbon dioxide reduction reaction (CO2RR) catalysts but also advances CO2 electrolysis technologies for industrial application.

First-principles study on the effects of fast neutron irradiation and fast neutron irradiation under the external electric field on carbon-based material AB bilayer graphene

The irradiation damage mechanism of fast neutron irradiation and the fast neutron irradiation under the practical application of an additional electric field on carbon-based material AB bilayer graphene is not yet clear. This paper systematically investigates the impact of fast neutron irradiation and fast neutron irradiation under the practical application of the additional electric field (−0.2 V/Å) on carbon-based material AB bilayer graphene through density functional theory and molecular dynamics simulations. The research results indicate that the changes in the configuration of AB bilayer graphene and the appearance of surface ripples induced by fast neutron irradiation are the two main reasons for the alterations in the system's microstructure, band structure, Young's modulus, and optical properties, which may lead to performance degradation and damage of carbon-based devices. The further variation in the average interlayer spacing of the system under external electric field irradiation leads to the diversity of the system configuration, which ultimately leads to the diversity of the band structure of the system. The uncertainty in the type and width of the bandgap in AB bilayer graphene under fast neutron irradiation with an external electric field may be one of the reasons for the performance degradation and permanent damage of carbon based devices in practical applications. In the fast neutron irradiation environment, the precise control of the bandgap of AB bilayer graphene by an applied electric field will fail.