Lattice-dynamics and thermal-conductivity calculations were performed using the Phonopy and Phono3py packages. The second-and third-order interatomic force constants (IFCs) were determined using the supercell finite-displacement method with displacement step sizes of 10 -2 and 3 × 10 -2 Å respectively. The second-order IFCs were determined in 2 × 2 × 2 supercells with 256/264 atoms, while the third-order IFCs were calculated in the base cells with 32/33 atoms. During the single-point force calculations an auxiliary charge-density grid with 8× the number of grid points was used to evaluate the forces, and the kpoint sampling for the 256/264-atom supercells was reduced proportionately to 2 × 2 × 2.