While it is well known that the vibrational modes are fully occupied and the quantum effect can be ignored only if the temperature is high enough, e.g., well above the Debye temperature of the systems, all vibrational modes are assumed to be fully occupied at any temperatures in classical molecular dynamics. Therefore, the thermal conductivity of crystals predicted by classical molecular dynamics at low temperatures, e.g., much lower than the corresponding Debye temperature, is unphysical. Even by applying the quantum corrections on the classical thermal conductivity of crystals, the results are still unreasonable since both the occupation and intrinsic scattering process of the vibrations are determined by the temperatures. However, the scattering picture in amorphous silicon is quite different from that in its corresponding crystal counterpart. How the quantum effect will affect the thermal transport in amorphous silicon is still unclear. Here, by systematically investigating thermal transport of amorphous silicon using equilibrium molecular dynamics, the structure factor method and the Allen–Feldman theory, we directly observe that all the vibrational modes are fully occupied at any temperatures and the quantum effect on the scattering process can be ignored. By assuming all the vibrational modes are fully occupied, the thermal conductivity calculated using the structure factor method and the Allen–Feldman theory agrees quite well with the results computed using Green–Kubo equilibrium molecular dynamics. By correcting the excitation state of the vibrations in amorphous silicon, the thermal conductivity calculated by the structure factor method and the Allen–Feldman theory can fully capture the experimentally measured temperature dependence. Our study proves that the quantum effect on the scattering process caused by the distribution functions for the amorphous materials in molecular dynamics simulations, i.e., Boltzmann distributions in molecular dynamics simulations vs Bose–Einstein distributions for the bosons, can be ignored, while the quantum effect on the excitation states of the vibrations are important and must be considered.
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21 June 2021
Research Article|
June 16 2021
Assessing the quantum effect in classical thermal conductivity of amorphous silicon
Yanguang Zhou
Yanguang Zhou
a)
Department of Mechanical and Aerospace Engineering, The Hong Kong University of Science and Technology
, Clear Water Bay, Kowloon, Hong Kong
a)Author to whom correspondence should be addressed: maeygzhou@ust.hk
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a)Author to whom correspondence should be addressed: maeygzhou@ust.hk
J. Appl. Phys. 129, 235104 (2021)
Article history
Received:
April 14 2021
Accepted:
May 30 2021
Citation
Yanguang Zhou; Assessing the quantum effect in classical thermal conductivity of amorphous silicon. J. Appl. Phys. 21 June 2021; 129 (23): 235104. https://doi.org/10.1063/5.0054039
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