To calculate the second-and third-order force constants (FCs) needed to compute the lattice thermal conductivity, we employed the finite-displacement method as implemented in the Phonopy and Phono3py packages. A 1100-atom 5 × 5 × 2 supercell based on the conventional unit cell was used to compute the second-order FCs, while a smaller 704-atom 4 × 4 × 2 supercell was used to evaluate the third-order FCs. The convergence of the phonon dispersion with respect to the supercell size used to compute the second-order FCs was explicitly checked. In total 19,743 displacements were evaluated to compute the third-order FCs in our chosen 4 × 4 × 2 supercell, using the default displacement distance of 0.03 A. The PBEsol functional was used for the phonon and thermal-conductivity calculations, as it has been shown to balance computational cost and accuracy to provide a good description of the lattice dynamics. A non-analytical correction (NAC) to treat the long-range interaction between the charges on the ions and the macroscopic electric field was also included.