Quantitatively analyzing phonon spectral contribution of thermal conductivity based on nonequilibrium molecular dynamics simulations. I. From space Fourier transform

Zhou, Yanguang; Zhang, Xiaoliang; Hu, Ming

doi:10.1103/physrevb.92.195204

Cited by 76 publications

(41 citation statements)

References 54 publications

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“…Therefore, only the small region near the sample affects the simulation results. This phenomenon is consistent with the findings in previous studies in which the length of the thermal reservoirs did not influence the results when it exceeded a critical value, which depended on the time parameter of the thermostat [24,32,37]. In contrast, for the NHC thermostat in Fig.…”

Section: The Effects Of Thermal Reservoir Size and Boundarysupporting

confidence: 92%

Unification of nonequilibrium molecular dynamics and the mode-resolved phonon Boltzmann equation for thermal transport simulations

Feng

et al. 2020

Phys. Rev. B

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Nano-size confinement induces many intriguing non-Fourier heat conduction phenomena, such as nonlinear temperature gradients, temperature jumps near the contacts, and size-dependent thermal conductivity. Over the past decades, these effects have been studied and interpreted by nonequilibrium molecular dynamics (NEMD) and phonon Boltzmann transport equation (BTE) simulations separately, but no theory that unifies these two methods has ever been established. In this work, we unify these methods using a quantitative mode-level comparison and demonstrate that they are equivalent for various thermostats. We show that different thermostats result in different non-Fourier thermal transport characteristics due to the different mode-level phonon excitations inside the thermostats, which explains the different size-dependent thermal conductivities calculated using different reservoirs, even though they give the same bulk thermal conductivity. Specifically, the Langevin thermostat behaves like a thermalizing boundary in phonon BTE and provides mode-level thermal-equilibrium phonon outlets, while the Nose-Hoover chain thermostat and velocity rescaling method behave like biased reservoirs, which provide a spatially uniform heat generation and mode-level nonequilibrium phonon outlets. These findings explain why different experimental measurement methods can yield different size-dependent thermal conductivity. They also indicate that the thermal conductivity of materials can be tuned for various applications by specifically designing thermostats. The unification of NEMD and phonon BTE will largely facilitate the study of thermal transport in complex systems in the future by, e.g., replacing computationally unaffordable first-principles NEMD simulations with computationally less expensive spectral BTE simulations.

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Section: The Effects Of Thermal Reservoir Size and Boundarysupporting

confidence: 92%

Unification of nonequilibrium molecular dynamics and the mode-resolved phonon Boltzmann equation for thermal transport simulations

Feng

et al. 2020

Phys. Rev. B

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“…Generally speaking, there is always length effect in NEMD simulations, since the long mean free path phonons are truncated by the length boundaries and contribute little to the overall thermal conductivity 35 . For NWs with cross-sections of a few nanometers, the mean free path (MFP) is only several nanometers 36 .…”

Section: Simulation Resultsmentioning

confidence: 99%

“…F. Alvarez et al 50 considered the size effect via doing the moment expansion of linearized Boltzmann transport equation in the relaxation time approximation, and found that the effective thermal conductivity will increase and then converge with the effective length. In the system with small effective length (dozens of nanometers in our paper), the thermal conductivity will be size dependent due to the fact that the phonons with MFP larger than the system will be truncated and have no contribution to the total thermal conductivity 35 . Recently, Hua and Cao 51 generated a theory based on the phonon BTE to study the influence of boundary constraints on thermal conductivity of NWs.…”

Section: Simulation Resultsmentioning

confidence: 99%

Strong Surface Orientation Dependent Thermal Transport in Si Nanowires

Zhou

Chen

2016

Sci Rep

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Thermoelectrics, which convert waste heat to electricity, offer an attractive pathway for addressing an important niche in the globally growing landscape of energy demand. Research to date has focused on reducing the thermal conductivity relative to the bulk. Si nanowires (NWs) have received exceptional attention due to their low-dimensionality, abundance of availability, and high carrier mobility. From thermal transport point of view, the thermal conductivity of Si NWs strongly depends on the detailed surface structure, such as roughness and surface orientation. Here, direct molecular dynamics simulations and theoretical models are used to investigate the thermal transport in Si NWs with diverse surface orientations. Our results show that the thermal conductivity of Si NWs with different surface orientation can differ by as large as 2.7~4.2 times, which suggests a new route to boost the thermoelectric performance. Using the full spectrum theory, we find that the surface orientation, which alters the distribution of atoms on the surface and determines the degree of phonon coupling between the core and the surface, is the dominant mechanism. Furthermore, using spectral thermal conductivity, the remarkable difference in the thermal conductivity for different surface orientation is found to only stem from the phonons in the medium frequency range, with minor contribution from low and high frequency phonons.

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“…Molecular dynamics simulations [7,8] have allowed the overall value of the TBR to be computed, including the full anharmonicity of the interatomic potential. Mode-resolved techniques [9][10][11][12][13][14] were recently developed to investigate how specific phonon modes are affected by interfaces. However, the typical wave packet approach is extremely computationally expensive for many modes in a Brillouin zone grid.…”

Section: Introductionmentioning

confidence: 99%

Ab initio study of mode-resolved phonon transmission at Si/Ge interfaces using atomistic Green's functions

2017

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Solid interfaces with exceptionally low or high thermal conductance are of intense scientific and practical interest. However, realizing such interfaces is challenging due to a lack of knowledge of the phonon transmission coefficients between specific modes on each side of the interface and how the coefficients are affected by atomic scale structure. Here, we report an ab initio based study of phonon transmission at Si/Ge interfaces using a recent extension of the atomistic Green's function method that resolves transmission coefficients by mode. These results provide a detailed framework to investigate the precise transmission and reflection processes that lead to thermal resistance and how they depend on phonon frequency as well as incident angle. We find that the transmission and reflection processes can be partly explained with familiar concepts such as conservation of transverse momentum, but we also find that numerous phonons have zero transmission coefficient despite the existence of modes that satisfy transverse momentum conservation. This work provides detailed insights into precisely which phonons transmit or reflect at interfaces, knowledge necessary to design solid interfaces with extreme values of thermal conductance for thermoelectricity and heat management applications.

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Quantitatively analyzing phonon spectral contribution of thermal conductivity based on nonequilibrium molecular dynamics simulations. I. From space Fourier transform

Cited by 76 publications

References 54 publications

Unification of nonequilibrium molecular dynamics and the mode-resolved phonon Boltzmann equation for thermal transport simulations

Unification of nonequilibrium molecular dynamics and the mode-resolved phonon Boltzmann equation for thermal transport simulations

Strong Surface Orientation Dependent Thermal Transport in Si Nanowires

Ab initio study of mode-resolved phonon transmission at Si/Ge interfaces using atomistic Green's functions

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