88 research outputs found
Phonon Transport Simulator (PhonTS)
No full textThis program has been imported from the CPC Program Library held at Queen's University Belfast (1969-2018)
Abstract
Thermal conductivity prediction remains an important subject in many scientific and engineering areas. Only recently has such prediction become possible on the basis of the first principles calculations, thus ensuring high quality results. Implementation of the methodology, however, is technically challenging and requires a lengthy development process. We thus introduce the Phonon Transport Simulator (PhonTS), a Fortran90, fully parallel code to perform such calculations. PhonTS possesses a l...
Title of program: PhonTS
Catalogue Id: AEVO_v1_0
Nature of problem
Computes thermal conductivity in crystal solids from the level of the interatomic interactions.
Versions of this program held in the CPC repository in Mendeley Data
AEVO_v1_0; PhonTS; 10.1016/j.cpc.2015.01.008
AEVO_v1_0; PhonTS; 10.1016/j.cpc.2015.01.00
First-principles Study on Pressure Induced Structural and Electronic Properties of Mg 1−xFexO using HSE06 and GGA+U Methods, a Combined Study
No full textWe investigate the pressure-induced spin crossover in ferropericlase (Mg1 − xFex O, x = 0.031 25–0.25) using first-principles calculations with generalized gradient approximation (GGA+U) and HSE06 methods. By analyzing spin transition pressures, structural distortions, and electronic properties, we establish a correspondence between the Hubbard U and hybrid mixing parameter α. Both methods predict a linear increase in transition pressure with Fe concentration and show weak sensitivity to Fe distribution. Our findings clarify the strengths and limitations of each approach and provide guidance for modeling spin transitions in mantle materials
A Molecular Dynamics Study of Tilt Grain Boundary Resistance to Slip and Heat Transfer in Nanocrystalline Silicon
No full textWe present a molecular dynamics study of grain boundary (GB) resistance to dislocation-mediated slip transfer and phonon-mediated heat transfer in nanocrystalline silicon bicrystal. Three most stable (110) tilt GBs in silicon are investigated. Under mechanical loading, the nucleation and growth of hexagonal-shaped shuffle dislocation loops are reproduced. The resistances of different GBs to slip transfer are quantified through their constitutive responses. Results show that the Σ3 coherent twin boundary (CTB) in silicon exhibits significantly higher resistance to dislocation motion than the Σ9 GB in glide symmetry and the Σ19 GB in mirror symmetry. The distinct GB strengths are explained by the atomistic details of the dislocation-GB interaction. Under thermal loading, based on a thermostat-induced heat pulse model, the resistances of the GBs to transient heat conduction in ballistic-diffusive regime are characterized. In contrast to the trend found in the dislocation-GB interaction in bicrystal models with different GBs, the resistances of the same three GBs to heat transfer are strikingly different. The strongest dislocation barrier Σ3 CTB is almost transparent to heat conduction, while the dislocation-permeable Σ9 and Σ19 GBs exhibit larger resistance to heat transfer. In addition, simulation results suggest that the GB thermal resistance not only depends on the GB energy but also on the detailed atomic structure along the GBs
Uncertainty Quantification in Multiscale Simulation of Materials: A Prospective
No full textSimulation has long since joined experiment and theory as a valuable tool to address materials problems. Analysis of errors and uncertainties in experiment and theory is well developed; such analysis for simulations, particularly for simulations linked across length scales and timescales, is much less advanced. In this prospective, we discuss salient issues concerning uncertainty quantification (UQ) from a variety of fields and review the sparse literature on UQ in materials simulations. As specific examples, we examine the development of atomistic potentials and multiscale simulations of crystal plasticity. We identify needs for conceptual advances, needs for the development of best practices, and needs for specific implementations
A Symmetry-Oriented Crystal Structure Prediction Method for Crystals with Rigid Bodies
No full textWe have developed an efficient crystal structure prediction (CSP) method for desired chemical compositions, specifically suited for compounds featuring recurring molecules or rigid bodies. We applied this method to two metal chalcogenides: Li3PS4and Na6Ge2Se6, treating PS4as a tetrahedral rigid body and Ge2Se6as an ethane-like dimer rigid body. Initial trials not only identified the experimentally observed structures of these compounds but also uncovered several novel phases, including a new stannite-type Li3PS4structure and a potential stable structure for Na6Ge2Se6that exhibits significantly lower energy than the observed phase, as evaluated by density functional theory calculations. We compared our results with those obtained using USPEX, a popular CSP package leveraging genetic algorithms. Both methods predicted the same lowest energy structures in both compounds. However, our method demonstrated better performance in predicting metastable structures. the method is implemented with Python code which is available athttps://github.com/ColdSnaap/sgrcsp.git
A symmetry-oriented crystal structure prediction method for crystals with rigid bodies
No full textWe have developed an efficient crystal structure prediction (CSP) method for desired chemical compositions, specifically suited for compounds featuring recurring molecules or rigid bodies. We applied this method to two metal chalcogenides: and , treating as a tetrahedral rigid body and as an ethane-like dimer rigid body. Initial trials not only identified the experimentally observed structures of these compounds but also uncovered several novel phases, including a new stannite-type structure and a potential metastable structure for that exhibits significantly lower energy than the observed phase, as evaluated by density functional theory (DFT) calculations. We compared our results with those obtained using USPEX, a popular CSP package leveraging genetic algorithms. Both methods predicted the same lowest energy structures in both compounds. However, our method demonstrated better performance in predicting metastable structures. The method is implemented with Python code which is available at https://github.com/ColdSnaap/sgrcsp.git
Evaluation of Computational Techniques for Solving the Boltzmann Transport Equation for Lattice Thermal Conductivity Calculations
No full textThree methods for computing thermal conductivity from lattice dynamics (the iterative method, the variational method, and the relaxation-time approximation) are compared for the prototypical case of solid argon. The iterative method is found to produce results in close agreement with Green-Kubo molecular-dynamics simulations, a formally correct method for computing thermal conductivity. The variational method and relaxation-time approximation are found to underestimate the thermal conductivity. The relationship among the methods is established; a combination of the iterative and variational methods is found to have a fastest convergence. Formal convergence of the iterative method is demonstrated and a simple mixing rule is shown to provide stability in practice. The ability to use these methods to provide detailed insight into the relationship between phonon properties and thermal conductivity is demonstrated
Threshold Displacement Energies And Primary Radiation Damage In AlN From Molecular Dynamics Simulations
No full textAluminum nitride (AlN) is an attractive material for sensing application in radiation environments owing to its radiation resistance, optical wide-bandgap, and piezoelectric properties. Yet, the variations of its physical properties under exposure to energetic particle needs to be better understood. Here, we report the results of the molecular dynamics simulations of the structural changes in AlN under irradiation via the knock-on atom technique. By creating and evolving irradiation cascades due to energetic particle interactions with the atoms of the crystalline lattice, we determine the rate of defect production as a function of the deposited energy. Further, we determine the threshold displacement energy, a key characteristic that describes how efficient the defect production in the given material is. We find that displacement threshold is slightly greater than isostructural gallium nitride and is lower than metal oxides used in radiation environments
A Coherent Phonon Pulse Model for Transient Phonon Thermal Transport
No full textIn this work, we present a novel heat source model, the coherent phonon pulse (CPP), composed of spatiotemporal Gaussian wave packets to mimic the coherent excitation of a non-equilibrium phonon population by ultrashort laser techniques, for the study of transient phonon thermal transport. Through molecular dynamic simulations of phonon transport in bicrystalline silicon-nanowires containing Σ3 and Σ19 grain-boundaries (GBs), we demonstrate that the new model facilitates not only a quantitative measurement of phonon-interface scattering, but also a mechanistic understanding of the highly non-equilibrium process of phonon transport with the coherent wave nature being preserved
Elastic and thermal properties of hexagonal perovskites
No full textWe systematically investigate the mechanical and thermal properties of the P6₃cm hexagonal perovskites with composition A³+B³+O₃ for potential use in thermal barrier coatings. In spite of the structural anisotropy, the elastic constants are essentially isotropic. The thermal expansion is, however, strongly anisotropic, while the thermal conductivity is relatively isotropic. The thermal conductivities of the hexagonal perovskites are much larger than those of the orthorhombic perovskites
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