Molecular simulations and lattice dynamics determination of Stillinger-Weber GaN thermal conductivity

Abstract

The bulk thermal conductivity of Stillinger-Weber (SW) wurtzite GaN in the [0001] direction at a temperature of 300 K is calculated using equilibrium molecular dynamics (EMD), non-equilibrium MD (NEMD), and lattice dynamics (LD) methods. While the NEMD method predicts a thermal conductivity of 166 6 11 W/mÁK, both the EMD and LD methods predict thermal conductivities that are an order of magnitude greater. We attribute the discrepancy to significant contributions to thermal conductivity from long-mean free path phonons. We propose that the Gr€ uneisen parameter for low-frequency phonons is a good predictor of the severity of the size effects in NEMD thermal conductivity prediction. For weakly anharmonic crystals characterized by small Gr€ uneisen parameters, accurate determination of thermal conductivity by NEMD is computationally impractical. The simulation results also indicate the GaN SW potential, which was originally developed for studying the atomic-level structure of dislocations, is not suitable for prediction of its thermal conductivity.

Equivalence of the equilibrium and the nonequilibrium molecular dynamics methods for thermal conductivity calculations: From bulk to nanowire silicon

“…Therefore, no matter what expression is used in the fit, using NEMD data with relatively short simulation cell lengths may result in significant errors and is a possible reason for some reported inconsistencies between the EMD and NEMD methods. Recently, Liang et al [18] found that the extrapolated κ 0 obtained by using the linear fit to their NEMD data with L x ≤ 150 nm is 166 ± 11 W m −1 K −1 for bulk GaN (described by a SW potential) at 300 K, which is several times smaller than their EMD value, 1190 ± 85 W m −1 K −1 . They also attributed the inconsistency between the NEMD and EMD predictions to the inadequacy of the linear extrapolation.…”

Intrinsic nanotwin effect on thermal boundary conductance in bulk and single-nanowire twinning superlattices

“…Here, simulations were repeated with different heat exchanges (J = 9.5 -18 eV•ps -1 ). Cross-plane and in-plane thermal conductivities, denoted in the following with superscript symbols ⊥ and ||, respectively, were measured perpendicular and parallel to the interfaces along [ ] Scaling effects on thermal conductivity computed from MD simulations, particularly the differences between NEMD and equilibrium (EMD) methods, have received considerable attention in the literature [40,42,43]. For the NEMD method, a sizeindependent thermal conductivity is usually obtained by performing a linear extrapolation from multiple systems of different length [40].…”

“…Scaling effects on thermal conductivity computed from MD simulations, particularly the differences between NEMD and equilibrium (EMD) methods, have received considerable attention in the literature [40,42,43]. For the NEMD method, a sizeindependent thermal conductivity is usually obtained by performing a linear extrapolation from multiple systems of different length [40].…”

First-principle-based full-dispersion Monte Carlo simulation of the anisotropic phonon transport in the wurtzite GaN thin film

“…This was also found by Liang et al using the nonequilibrium molecular dynamic method. 33 Results in Fig. 6(a) indicate that the anisotropy is reduced with decreasing film thickness and even disappear when the size effect is very strong.…”