Stacking-dependent phonon scattering and low-dimensional thermal transport in bilayer PtX2 (X = S, Se): A first-principles study

We present a comprehensive study of the thermal transport properties of bilayer PtX₂ (X = S, Se) with focus on the influence of stacking configurations and interlayer interactions. Two common stacking orders (AA and AB) were investigated with the first-principles calculations of phonon dispersions, group velocities, and scattering rates. These structural differences affect the phonon spectra, and exhibit characteristic shifts in the group velocities. Thermal transport calculations using both the relaxation time approximation and the full linearized Boltzmann transport equation reveal that the relaxation time approximation underestimates thermal conductivities, due to its limited treatment of normal scattering processes which are more distinct in the AA stacking as a consequence of strong interlayer interactions. Mode-dependent and cumulative thermal conductivity analyses elucidate the individual contributions of the different phonon modes and frequency ranges to the thermal transport properties.