Lattice-dynamics and thermal-conductivity calculations were set up and postprocessed using the Phonopy and Phono3py software. The second-and thirdorder force constants (FC2/FC3) were determined using the supercell finite-displacement method, with 6×6×2 expansions of the conventional cell (720 atoms) and a displacement step of 10 -2 Å for the FC2 and 3 × 3 × 1 expansions (90 atoms) and a step size of 3 × 10 -2 Å for the FC3. During the single-point force calculations additional support grids with 8 × the number of points as the standard charge-density grids were employed to reduce numerical noise (ADDGRID = .TRUE.). Phonon density of states (DoS) curves g(ν) were computed by interpolating the phonon frequencies onto the regular Γ-centered 24 × 24 × 24 q-point grids and applying a Gaussian smearing with a width σ = 0.064 THz, corresponding to a full-width at half-maximim (FWHM) of 5 cm -1 . Phonon dispersion curves ν(q) were computed by interpolating frequencies along strings of qpoints passing between high-symmetry wavevectors in the I4/mmm Brillouin zone. The lattice thermal conductivities were computed using the single-mode relaxation-time approximation (SM-RTA) from modal properties evaluated on regular 16 × 16 × 16 q-point meshes. This mesh was chosen based on explicit testing to converge the κ latt to within ∼ 3% of the values obtained with larger 24 × 24 × 24 sampling meshes. For the phonon dispersion and κ latt calculations, a conversion to the primitive cell was performed using the transformation matrix: