Browsing by Subject "molecular dynamics"

Now showing 1 - 4 of 4
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    Atomistic Modeling of Anisotropic Mechanical Properties of Lanthanum Zirconate Nanocystal
    (Elsevier, 2021-02) Guo, Xingye; Zhang, Jian; Park, Hye-Yeong; Jung, Yeon-Gil; Zhang, Jing; Mechanical and Energy Engineering, School of Engineering and Technology
    Lanthanum zirconate (La2Zr2O7, or LZ) has been widely recognized as a promising candidate material for thermal barrier coating (TBC) applications since it has low thermal conductivity, high-temperature phase stability, and low sintering activity. However, the mechanical properties of LZ crystal have not been fully understood, which hinders it from future applications. In this work, atomistic simulations were performed to study the anisotropic mechanical properties of LZ crystal. Using both the first principles and molecular dynamics (MD) calculations, uniaxial tensile tests of LZ crystal in [001], [011], and [111] directions were simulated. The stress-strain curves of the tensile tests were calculated, and the ultimate tensile strength and toughness were derived. The Young's moduli in [001], [011], and [111] directions were calculated using both the stress-strain curves and an analytical method for small deformation. Additionally, shear stress-strain curves in {111}<110> and {111}<112> directions were investigated using both the first principles calculations and the MD method. Results show that Young's modulus of LZ crystal is highly anisotropic. The crystal has the highest Young's modulus in [111] direction, and {111}<112> direction is the favorable slip system during shear deformations.
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    Atomistic modeling of resistivity evolution of copper nanoparticle in intense pulsed light sintering process
    (Elsevier, 2019-02) Meng, Lingbin; Zhang, Yi; Yang, Xuehui; Zhang, Jing; Mechanical and Energy Engineering, School of Engineering and Technology
    In this work, the intense pulsed light (IPL) sintering process of copper nanoparticle ink is simulated using molecular dynamics (MD) method. First, the neck size growth between the two copper nanoparticles during the IPL sintering process is computed. The resultant electrical resistivity is then calculated by substituting the neck size into the Reimann-Weber formula. Overall, a rapid decrease of electric resistivity is observed in the beginning of the sintering, which is caused by quick neck size growth, followed by a gradually decrease of resistivity. In addition, the correlation of the simulated temperature dependent resistivity is similar to that of the experimentally measured resistivity. The MD model is an effective tool for designers to optimize the IPL sintering process.
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    A Computational Study of the Mechanism for F1-ATPase Inhibition by the Epsilon Subunit
    (2013) Thomson, Karen J.; Pu, Jingzhi; Ge, Haibo; Sardar, Rajesh; Long, Eric C. (Eric Charles)
    The multi-protein complex of F0F1 ATP synthase has been of great interest in the fields of microbiology and biochemistry, due to the ubiquitous use of ATP as a biological energy source. Efforts to better understand this complex have been made through structural determination of segments based on NMR and crystallographic data. Some experiments have provided useful data, while others have brought up more questions, especially when structures and functions are compared between bacteria and species with chloroplasts or mitochondria. The epsilon subunit is thought to play a signi cant role in the regulation of ATP synthesis and hydrolysis, yet the exact pathway is unknown due to the experimental difficulty in obtaining data along the transition pathway. Given starting and end point protein crystal structures, the transition pathway of the epsilon subunit was examined through computer simulation.The purpose of this investigation is to determine the likelihood of one such proposed mechanism for the involvement of the epsilon subunit in ATP regulation in bacterial species such as E. coli.
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    Molecular Dynamics Simulations of the Mechanical Deformation Behavior of Face-Centered Cubic Metallic Nanowires
    (2010-05-05T14:41:16Z) Heidenreich, Joseph David; Wang, Guofeng; Chen, Jie; Jones, Alan
    Nanoscale materials have become an active area of research due to the enhanced mechanical properties of the nanomaterials in comparison to their respective bulk materials. The effect that the size and shape of a nanomaterial has on its mechanical properties is important to understand if these materials are to be used in engineering applications. This thesis presents the results of molecular dynamics (MD) simulations on copper, gold, nickel, palladium, platinum, and silver nanowires of three cross-sectional shapes and four diameters. The cross-sectional shapes investigated were square, circular, and octagonal while the diameters varied from one to eight nanometers. Due to a high surface area to volume ratio, nanowires do not have the same atomic spacing as bulk materials. To account for this difference, prior to tensile loading, a minimization procedure was applied to find the equilibrium strain for each structure size and shape. Through visualization of the atomic energy before and after minimization, it was found that there are more than two energetically distinct areas within the nanowires. In addition, a correlation between the anisotropy of a material and its equilibrium strain was found. The wires were then subjected to a uniaxial tensile load in the [100] direction at a strain rate of 108 s-1 with a simulation temperature of 300 K. The embedded-atom method (EAM) was employed using the Foiles potential to simulate the stretching of the wires. The wires were stretched to failure, and the corresponding stress-strain curves were produced. From these curves, mechanical properties including the elastic modulus, yield stress and strain, and ultimate strain were calculated. In addition to the MD approach, an energy method was applied to calculate the elastic modulus of each nanowire through exponential fitting of an energy function. Both methods used to calculate Young’s modulus qualitatively gave similar results indicating that as diameter decreases, Young’s modulus decreases. The MD simulations were also visualized to investigate the deformation and yield behavior of each nanowire. Through the visualization, most nanowires were found to yield and fail through partial dislocation nucleation and propagation leading to {111} slip. However, the 5 nm diameter octagonal platinum nanowire was found to yield through reconstruction of the {011} surfaces into the more energetically favorable {021} surfaces.