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Anharmonic force constants extracted from first-principles molecular dynamics: applications to heat transfer
T Tadano1, Y Gohda, S Tsuneyuki
1Department of Physics, The University of Tokyo, Tokyo 113-0033, Japan.
This study presents a new method for calculating crystal anharmonic force constants using molecular dynamics. The approach accurately predicts thermal conductivity in silicon and thermoelectric materials.
Area of Science:
- Condensed Matter Physics
- Materials Science
- Computational Physics
Background:
- Accurate calculation of anharmonic force constants is essential for understanding thermal transport in crystals.
- First-principles molecular dynamics (MD) simulations offer a powerful tool for investigating these properties.
Purpose of the Study:
- To develop and validate a systematic method for calculating anharmonic force constants.
- To investigate the thermal conductivity of silicon (Si) and magnesium silicide (Mg2Si) using the derived force constants.
Main Methods:
- Employed the direct-method approach with first-principles molecular dynamics simulations at high temperatures.
- Extracted anharmonic force constants from MD trajectories, incorporating higher-order corrections for large atomic displacements.
- Combined calculated force constants with the Boltzmann transport equation (BTE) and non-equilibrium molecular dynamics (NEMD) for thermal conductivity calculations.
Main Results:
- Obtained accurate cubic and quartic anharmonic force constants for Si.
- BTE successfully predicted Si's lattice thermal conductivity, while NEMD showed underestimates due to nonlinear size dependence.
- Demonstrated the reliability of NEMD for low thermal conductivity systems like Mg2Si.
Conclusions:
- Higher-order corrections are crucial for accurate anharmonic force constants from MD simulations with large displacements.
- BTE is a reliable method for predicting lattice thermal conductivity in bulk materials.
- NEMD requires careful analysis of size dependence, especially for materials with long-mean-free-path acoustic phonons.
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