Research

"Lattice thermal conductivity calculated with first-principles anharmonic lattice model"

Lattice thermal conductivity is an important parameter determining the figure of merit in thermoelectric materials. As a computational approach to estimate the thermal conductivity, Boltzmann transport equation with relaxation time approximation has been widely used. But this method has theoretical difficulties in treating scattering effects by surfaces, interfaces and impurities. (Non-equilibrium) molecular dynamics is another method to calculate the lattice thermal conductivity and it is applicable to any complex systems. However, it cannot be combined with first-principles molecular dynamics because of its high computational cost arising from the long simulation time and the large number of atoms required. Thus, its application has been limited to the specific materials where well-established classical model potential can be utilized.

In order to calculate the lattice thermal conductivity of materials regardless of their chemical composition without empirical parameters, we have established a general method to construct anharmonic lattice model which can be used in any materials and structures, and developed a new method for calculating the lattice thermal conductivity which utilize the anharmonic lattice model and non-equilibrium molecular dynamics. Anharmonic lattice model contains harmonic, cubic and quartic interatomic force constants and they were determined by first-principles calculations. We have applied our method to silicon and diamond and investigated the validity of the method. As a result, we have obtained reasonable values for the bulk thermal conductivity [1]. Also, non-linear size dependence of the thermal conductivity was observed. This is a characteristic behavior of quasi-ballistic heat transport where the system size and the phonon mean free path are comparable.

 

[1] T. Tadano, Y. Gohda, S. Tsuneyuki, in preparation.

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