Argon Thermal Conductivity by Anharmonic Lattice Dynamics Calculations

2008 ◽  
Author(s):  
J. E. Turney ◽  
A. J. H. McGaughey ◽  
C. H. Amon
Keyword(s):  
Thermal Conductivity ◽  
Thermal Transport ◽  
Lattice Dynamics ◽  
Mode Shapes ◽  
Face Centered Cubic ◽  
Phonon Modes ◽  
Anharmonic Lattice ◽  
The Face ◽  
Face Centered ◽  
Dynamics Simulations

Lattice dynamics calculations are used to investigate thermal transport in the face-centered cubic Lennard-Jones (LJ) argon crystal between temperatures of 20 and 80 K. First, quasi-harmonic lattice dynamics calculations are used to find the frequencies and mode shapes of non-interacting phonons [1]. This information is then used as input for anharmonic lattice dynamics calculations. Anharmonic lattice dynamics is a means of computing the frequency shift and lifetime of each phonon mode due to interactions with other phonons [2]. The phonon frequencies, group velocities, and lifetimes, determined with the lattice dynamics methods, are then used to compute the thermal conductivity. The thermal conductivities predicted by the lattice dynamics methods are compared to predictions from molecular dynamics simulations. The two methods are found to agree well at low temperature but diverge at higher temperatures (i.e., near the melting point). The properties of individual phonon modes are used to identify the modes that dominate thermal transport.

Thin Film Thermal Conductivity by Anharmonic Lattice Dynamics Calculations

2008 ◽  
Author(s):  
J. E. Turney ◽  
A. J. H. McGaughey ◽  
C. H. Amon
Keyword(s):  
Thin Film ◽  
Thin Films ◽  
Thermal Conductivity ◽  
Lattice Dynamics ◽  
Phonon Mode ◽  
Mode Shapes ◽  
Bulk Crystals ◽  
Anharmonic Lattice ◽  
Dynamics Simulations ◽  
Group Velocities

Lattice dynamics calculations are used to investigate thermal transport in argon thin films with thicknesses ranging between one and ten nanometers. Quasi-harmonic lattice dynamics calculations are used to find the frequencies and mode shapes of non-interacting phonons. This information is then used as input for anharmonic lattice dynamics calculations, whereby we compute the frequency shift and lifetime of each phonon mode due to interactions with other phonons. The phonon frequencies, group velocities, and lifetimes determined with the lattice dynamics techniques are then used to compute the in-plane thermal conductivity of the thin films as a function of film thickness. The thermal conductivities predicted by the lattice dynamics methods are compared to predictions from molecular dynamics simulations. Differences in the phonon characteristics in thin films compared to bulk crystals are examined by comparing the contribution to the thermal conductivity as a function of frequency.

Investigation of Crystalline and Amorphous Forms of Aluminum and Its Alloys: Computational Modeling and Experiment

NANO ◽  
2018 ◽  
Vol 13 (03) ◽  
pp. 1850026
Author(s):  
Sergey Shityakov ◽  
Norbert Roewer ◽  
Carola Y. Förster ◽  
Hai T. Tran ◽  
Wenjun Cai ◽  
...  
Keyword(s):  
Metal Structure ◽  
Dislocation Nucleation ◽  
Al Alloys ◽  
Atomic Scale ◽  
Face Centered Cubic ◽  
Stress Strain ◽  
The Face ◽  
Tension And Compression ◽  
Face Centered ◽  
Dynamics Simulations

The purpose of this study is to investigate polycrystalline lattices of aluminum (Al) under the stress–strain conditions in all-atom molecular dynamics simulations and Al alloys using X-ray diffraction. Isothermal uniaxial tension and compression of these polycrystalline lattices showed no dislocation nucleation peaks, which correspond only to the Al monocrystal form. The best tensile and compressive resistance characteristics were observed for a material with the highest grain number ([Formula: see text]) due to the significant reduction of the face-centered cubic lattice in the metal structure. This process is mainly driven by the gradual elevation of the system’s kinetic energy. In the experiment, the amorphous Al alloys with higher manganese composition (20.5%) were investigated, matching the simulated amorphous structures. Overall, the results suggest that the increase in number of grains in Al lattices diminishes the stress–strain impact due to a more disordered atomic-scale (amorphous) metal composition.

Role of Edge Chirality and Isotope Doping in Thermal Transport and Thermal Rectification in Graphene Nanoribbons

2011 ◽  
Author(s):  
Yan Wang ◽  
Xiulin Ruan
Keyword(s):  
Thermal Conductivity ◽  
Thermal Transport ◽  
Graphene Nanoribbons ◽  
Mass Density ◽  
Transport Processes ◽  
Phonon Modes ◽  
Cross Sectional ◽  
Thermal Rectification ◽  
The Difference ◽  
Dynamics Simulations

Thermal transport processes in graphene nanoribbons (GNRs) within and beyond the linear response regime has been studied using classical molecular dynamics simulations. Zigzag-edged GNRs have higher thermal conductivities than armchair-edged ones, and the difference diminishes with increasing width. Analysis on the cross-sectional distribution of heat flux reveals that edge atoms cannot transport thermal energy as efficiently as interior ones. Edge localization of phonon modes reduces thermal transport through edge carbon atoms, especially on armchair edges, which results in a lower thermal conductivity. Isotope (13C) doping can reduce the thermal conductivity of GNRs by 30%–40% by an addition of only ∼20% isotope atoms. The significant reduction in thermal conductivity is partially attributed to phonon localization induced by isotope defects, which is confirmed by phonon mode participation ratio analysis. We also demonstrate that a GNR asymmetric in edge chirality or mass density can generate considerable thermal rectification, which is essential for developing GNR-based thermal management devices.

MOLECULAR DYNAMICS SIMULATIONS OF STRUCTURAL PROPERTIES OF CuNi ALLOYS DURING THE COOLING PROCESS AT HIGH PRESSURE

2020 ◽  
Vol 65 (10) ◽  
pp. 10-17
Author(s):  
Thao Nguyen Thi ◽  
Giang Bui Thi Ha ◽  
Linh Tran Phan Thuy ◽  
Hop Nguyen Van ◽  
Chung Pham Do ◽  
...  
Keyword(s):  
Molecular Dynamics ◽  
High Pressure ◽  
Molecular Dynamics Simulations ◽  
Sudden Change ◽  
Face Centered Cubic ◽  
Cooling Process ◽  
Embedded Atom ◽  
The Face ◽  
Face Centered ◽  
Dynamics Simulations

Molecular dynamics simulations of Cu80Ni20 (Cu:Ni = 8:2) model with the size of 8788 atoms have been carried out to study the structure and mechanical behavior at high pressure of 45 GPa. The interactions between atoms of the system were calculated by the Quantum Sutton-Chen embedded-atom potentials. The crystallization has occurred during the cooling process with a cooling rate of 0.01 K\ps. The temperature range of the phase transition is determined based on the sudden change of atomic potential during the cooling process. There is also a sudden change in the number of individual atoms in the sample. At a temperature of 300 K, both Ni and Cu atoms are crystallized into the face-centered cubic (FCC) and the hexagonal close-packed (HCP) phases, respectively. The mechanical characteristics of the sample at 300 K were also analyzed in detail through the determination of elastic modulus, number of atoms, and void distribution during the tensile process.

Thermal Transport in Graphene Supported on Copper

2012 ◽  
Author(s):  
Liang Chen ◽  
Satish Kumar
Keyword(s):  
Thermal Conductivity ◽  
Thermal Transport ◽  
Copper Substrate ◽  
Interaction Strength ◽  
Thermal Coupling ◽  
Phonon Modes ◽  
Large Wave ◽  
Relaxation Time Approximation ◽  
Out Of Plane ◽  
Dynamics Simulations

The present study investigates the thermal transport in suspended graphene and graphene supported on copper substrate using equilibrium molecular dynamics simulations, Green-Kubo method and relaxation time approximation (RTA) approach. The thermal coupling between graphene and copper substrate was investigated by varying the interaction strength between the carbon atoms and Cu atoms at the interface. The contribution of different phonon modes to the thermal conductivity of suspended and supported graphene was analyzed in order to elucidate the graphene-substrate thermal interactions. The thermal conductivity of graphene decreases with the increasing strength of the interfacial interaction. The analysis shows that the interactions with copper substrate can reduce the thermal conductivity by up to 44%. The decrease of thermal conductivity is primarily due to the suppression of contribution from out-of-plane acoustic (ZA) phonons in the large wave vector region.

Prediction of metastable phase formation in an immiscible Cu–Cr system from interatomic potential and ab initio calculation

2003 ◽  
Vol 18 (10) ◽  
pp. 2300-2303 ◽  
Author(s):  
H. R. Gong ◽  
L. T. Kong ◽  
B. X. Liu
Keyword(s):  
Ab Initio ◽  
Interatomic Potential ◽  
Metastable Phase ◽  
The Body ◽  
Face Centered Cubic ◽  
The Face ◽  
Bcc Structure ◽  
Face Centered ◽  
Dynamics Simulations ◽  
Cr System

Ab initio calculation was performed to predict the structures, lattice constants, and cohesive energies of metastable Cu75Cr25 and Cu50Cr50 phases. An n-body Cu–Cr potential was derived through fitting to some ab initio calculated results and was capable of reproducing some intrinsic properties of the Cu–Cr system. Based on the derived potential, molecular dynamics simulations predicted that for a Cu100−xCrx alloy, the face-centered-cubic structure is more stable than the body-centered-cubic (bcc) one when 0 ≤ x ≤ 25, while the bcc structure becomes energetically favored when 25 < x ≤ 100. Interestingly, the predictions match well with the experimental observations.

A study of interface sliding at F.C.C.-B.C.C. boundaries in a Cu-Zn alloy

1978 ◽  
Vol 36 (1) ◽  
pp. 422-423
Author(s):  
F. Monchoux ◽  
A. Rocher ◽  
J.L. Martin
Keyword(s):  
Face Centered Cubic ◽  
Creep Tests ◽  
High Voltage Electron Microscopy ◽  
Diffusion Treatment ◽  
Voltage Electron ◽  
The Face ◽  
Face Centered ◽  
Interface Sliding ◽  
Zn Alloy ◽  
Made In

Interphase sliding is an important phenomenon of high temperature plasticity. In order to study the microstructural changes associated with it, as well as its influence on the strain rate dependence on stress and temperature, plane boundaries were obtained by welding together two polycrystals of Cu-Zn alloys having the face centered cubic and body centered cubic structures respectively following the procedure described in (1). These specimens were then deformed in shear along the interface on a creep machine (2) at the same temperature as that of the diffusion treatment so as to avoid any precipitation. The present paper reports observations by conventional and high voltage electron microscopy of the microstructure of both phases, in the vicinity of the phase boundary, after different creep tests corresponding to various deformation conditions.Foils were cut by spark machining out of the bulk samples, 0.2 mm thick. They were then electropolished down to 0.1 mm, after which a hole with thin edges was made in an area including the boundary

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