Papers by Keyword: Molecular Dynamics

Abstract: This research work focuses on the atomic study of hexagonal titanium (Ti) in order to estimate the relative accuracy of DFT (Density Functional Theory) and Molecular Statics (MS) approaches to better understand the interactions between solute atoms and twins. Four twins (2 tensile twins and 2 compressive twins) were modeled and then doped with the following elements: hydrogen, oxygen, nitrogen, aluminum and vanadium (H, O, N, Al, V). The formation energies of the twins as well as the segregation energies of the solute atoms were calculated to better predict the concentration heterogeneities of these elements in the material and their possible influence on local mechanical properties.

Abstract: This study presents an atomistic analysis of the stress-strain characteristics in the laser powder bed fusion (LPBF) process for the AlSi10Mg alloy. The stress-strain response of printed components is investigated by introducing defects through molecular dynamics simulation. The simulation box dimensions for tensile tests and crack propagation are 152.416 Å, 201.228 Å, and 42.49 Å along the X, Y, and Z directions. Periodic boundary conditions are applied along all sides. A constant strain rate of 10⁹ s⁻¹ is applied along the Y-direction at a temperature of 300 K. The simulation results reveal that the maximum stress occurs at the initial time step, followed by a gradual decline as stress decreases and strain increases, indicating plastic deformation through dislocation slip. Dislocation Analysis (DXA) shows that dislocations increase with increasing strain. These findings enhance the understanding of the material's deformation behaviour and provide insights for optimizing its properties through laser processing parameters.

Abstract: Hydrogen represents a promising clean energy carrier with exceptional gravimetric energy density (120 MJ/kg) [1]. Metal hydrides offer superior hydrogen storage through chemical absorption at interstitial sites, enabling performance optimization via alloy composition [2,3]. However, Mg-based hydrides, despite their high capacity, exhibit limitations including strong Mg-H bonding and sluggish kinetics, necessitating elevated dehydrogenation temperatures (600-700 K) [4,5]. Molecular dynamics (MD) simulations provide detailed atomistic insights into mechanical behavior under hydrogenation conditions [6]. This investigation employs MD to elucidate the effects of hydrogenation on the mechanical properties of Mg-Pd-Ni ternary alloys, aiming to identify compositions with enhanced structural durability for practical hydrogen storage applications.

Abstract: Molecular dynamics (MD) simulation was used to explore how models of W-He respond to irradiation induced damage. Displacement cascades up to 10 keV recoil energy were simulated for W-Σ17 and W-Σ17-He models. The pre-existing He bubbles within and around the grain boundary region have a major effect on the number and distribution of surviving Frenkel pairs. Frenkel pairs increased as the energy of the primary knock-on atom (PKA) increased across all models. Models containing pre-existing He bubbles showed a significant reduction in the number of surviving vacancies/SIAs compared to those without He bubbles. A large portion of point defects accumulate at the grain boundary which acts as a sink for defects during the recrystallization phase. The presence of He bubbles within or near the grain boundary region facilitates the defects generation, absorbs residual point defects, and form clusters. When He bubbles are located around the grain boundary, the number of surviving vacancies/SIAs decreased by 23% to 60% compared to models without He bubbles. However, for models with He bubbles located within the grain boundary structure, a much more extensive reduction occurred compared to models without He bubbles, which is between the range of 76% to 92%.

Abstract: Elemi essential oil, extracted from the resin of the elemi tree (Canarium luzonicum), is highly valued for its distinctive aromatic and medicinal properties. Its complex composition includes various monoterpenes and sesquiterpenes such as α-phellandrene, limonene, and elemicin, which collectively contribute to its unique fragrance and therapeutic benefits. However, the oil’s susceptibility to environmental factors such as heat, light, and oxidation often leads to degradation and reduced efficacy. In this study, we investigated the encapsulation of elemi essential oil components within cyclodextrin metal-organic frameworks (CD-MOFs) using molecular docking and molecular dynamics (MD) simulations to assess adsorption behavior and complex stability. Significant variation in binding affinities was observed, with cis-sabinene exhibiting the strongest adsorption driven by favorable hydrophobic interactions within the CD-MOF cavity, while β-phellandrene demonstrated weaker binding attributed to less optimal molecular fit. MD simulations further confirmed the stable encapsulation of hydrophobic compounds, including d-limonene, α-elemol, α-phellandrene, and elemicin within the CD-MOF structure. Despite conformational adjustments during simulation, these complexes maintained high structural integrity, as evidenced by consistently low root-mean-square deviation (RMSD) and radius of gyration values. These results underscore the critical role of non-covalent interactions, particularly van der Waals forces, and reveal the inherent structural flexibility and robustness of CD-MOFs in accommodating diverse hydrophobic guest molecules. This work demonstrates the strong potential of CD-MOFs as versatile and effective carriers for the encapsulation and stabilization of hydrophobic essential oil components, paving the way for their application in advanced delivery systems across pharmaceutical, cosmetic, and food industries.

Abstract: Zeolitic-imidazolate frameworks (ZIFs) have shown promise in gas separation through membranes. Nevertheless, the potential of mixed-layer ZIFs to be tailored for targeted gas separation remains largely unexplored. This study aims to fill this research gap through a Molecular Dynamics (MD) study by proposing two molecular models for mixed-layer ZIFs and evaluating their effectiveness in H₂ and CO₂ separation. MD simulations are conducted to validate and assess the diffusion properties of H₂ and CO₂ within the mixed-layered ZIF models. The results demonstrate that H₂ has higher diffusivity than CO₂ within the proposed ZIF models. Mixed-layer ZIF-8/ZIF-7 exhibits higher diffusion coefficients for both H₂ (4.79 × 10^-9 m²/s) and CO₂ (8.13 × 10^-11 m²/s) compared to pure ZIF-8, attributed to increased pore flexibility from the ZIF-7 layer. However, this enhancement in diffusion comes at the cost of reduced selectivity due to broader pore size distribution. In contrast, mixed-layer ZIF-8(Zn)/ZIF-8(Co) demonstrates a substantial increase in H₂ diffusion (5.17 × 10^-9 m²/s) and an exceptional selectivity of 310.00 for H₂ over CO₂, owing to the altered framework flexibility from incorporating different metal ions. The study further explores the effect of different adsorbate molecular models, revealing that the H₂_COMPASS and CO₂_TRAPPE combination yields the highest H₂/CO₂ selectivity. Additionally, increased molecular loading enhances diffusion. These findings underscore the critical role of structural modifications and molecular model selection in optimizing ZIF-based materials for gas separation applications. The proposed models and simulation results offer a foundation for future studies and the development of efficient and sustainable gas capture technologies.

Abstract: The current study was carried out by determining structural and energetic parameters to theoretically validate the experimental results of the adsorption efficiency of amine-functionalized porous carbon for the elimination of Cu²⁺ ions and Pb²⁺ and detail the reaction mechanism in the aqueous medium. The Density Functional Theory calculations, molecular dynamics, and Monte Carlo simulations were used to investigate the adsorption enhancement mechanism. The calculations were performed using the Dmol3 module of the Materials Studio program (MatS) using the exchange-correlation function M-11L2. DFT calculations were determined for porous carbon (PC) and porous carbon functionalized by ethylene diamine (PC-ED). Indeed, this study aims to reveal the functionalization influence on improving the adsorption efficiency of Cu²⁺ and Pb²⁺ by porous carbon (PC). Overall, the study attempts to explain the experimental results of the improved interactivity of porous carbon functionalized by ethylene diamine concerning Cu²⁺ and Pb²⁺ ions, compared to the reactivity of these ions with the group carboxyl characterizes the porous carbon (PC). The Molecular dynamics and Monte Carlo simulations were used to clarify the interactions between Cu²⁺ or Pb²⁺ ions and porous carbon modelled in the presence or absence of ethylene diamine (PC–ED) function. Hence, the theoretical study showed that the presence of ethylene diamine (C₂H₄(NH₂)₂)_m forms more ligands towards the ions of metal M²⁺ with the interaction bounds lower than ≤ 2.5 Å. The same result is shown by the small adsorption energy obtained in the range of -1140 to -200 kcal/mol for and -1200 to -600 kcal/mol for Pb²⁺ and Cu²⁺, respectively. Therefore, more adsorption of Cu²⁺ and Pb²⁺ ions. The theoretical results obtained agree with the experimental results.

Abstract: This study investigates the mechanical behavior of single and multi-wall carbon nanotubes (SWCNT/MWCNT) during torsional loading using the molecular dynamics (MD) simulation technique. The open-source software Large-Scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) is utilized to conduct MD simulations to gain valuable insights into the response of pristine and defective carbon nanotubes. The torsional behavior of armchair SWCNTs with chiralities (5,5); (7,7); (10,10); (12,12) and (15,15) and zigzag SWCNTs (12,0); (17,0) and (22,0) is explored to understand the effect of chirality on the torsional properties. Furthermore, the impact of the aspect ratio is examined by varying the diameter of SWCNTs while keeping the length constant. The findings reveal a notable decrease in shear modulus with increasing tube diameter, providing a crucial understanding of the torsional behavior concerning SWCNT geometry. To assess the effect of vacancy defects, 1%, 2%, and 4% vacancy defects are introduced on (10,10) armchair SWCNTs, and their torsional response is analyzed. The predictions highlight a significant reduction in shear modulus by 25% for SWCNTs with the rising concentration of vacancy defects from 1% to 4%. Overall, this study contributes to a deeper comprehension of the mechanical properties of carbon nanotubes under torsional loading, paving the way for potential applications in nanotechnology and nanocomposite design.

Abstract: This study investigates the influence of α/β interface characteristics on the mechanical properties and plastic deformation behavior of titanium alloys, focusing on Ti-Al-V system. Molecular dynamics simulations of Ti-Al-V alloys with different gradient α/β interface models reveal that the linear gradient interface exhibits superior strength at ultra-low temperatures compared to "S" gradient and non-gradient models. Analysis indicates structural transitions primarily occur at the interface at 70 K. Dislocation analysis shows high strength of the linear gradient interface at 70 K and 0.01 K, with dislocations concentrated at the α/β interface. With the change of interface characteristics, the mechanical properties also exhibit gradient variations.

Abstract: This study presents a novel and straightforward model of a nanomotor capable of rotation propelled by friction at the solid-liquid interface. Within this nanosystem operating in a Rotary Electric Field (REF), a pristine carbon nanotube, electrically neutral, is infused with water, serving as the rotor. Polar molecules within the water rotate alongside the REF, generating interface friction that propels the nanotube rotor. Molecular dynamics simulations demonstrate that the nanomotor rapidly achieves a stable rotational frequency (SRF), typically within 200 ps in this investigation. Furthermore, each rotor tube possesses a maximum SRF value, denoted as ω_RMax. When the REF frequency (ω_E) exceeds ω_RMax, the rotor tube, water cluster, and REF exhibit varying rotational frequencies. It is also observed that the relationship between the rotor's SRF and ω_E conforms to an inverse square law when ω_E surpasses ω_RMax. The underlying mechanism is elucidated. These findings can inform the design of a rotary nanomotor constructed from water-filled carbon nanotubes, offering tunable SRF capabilities.