Unveiling the Role of Four-Phonon Scattering in Thermal Transport of Penta-XN ₂ (X = Pd, Pt) Monolayers: Insights from First-Principles Calculations

Understanding, accurately predicting, and controlling thermal transport in penta-2D materials are crucial for optimizing their applications in nanoelectronics and energy devices. To this end, we systematically elucidate the thermal conductivity modulation in penta-XN2 (X = Pd, Pt) monolayers via first-principles calculations and four-phonon (4ph) scattering mechanisms. Penta-PtN2 exhibits faster acoustic phonon velocities, weaker anharmonicity, and higher intrinsic thermal conductivity compared to penta-PdN2. The inclusion of 4ph scattering significantly reduces thermal conductivity across the entire temperature range, as exemplified by reductions of 82% and 71% for penta-PdN2 and penta-PtN2, respectively, at 300 K. This reduction is primarily attributed to the redistribution channel of the normal process, which disrupts phonon transport by altering phonon populations, breaking transport directionality, and reducing coherence. This study unambiguously identifies the 4ph scattering under momentum conservation as the key factor limiting thermal conductivity in penta-XN2, providing theoretical guidance for optimizing strong anharmonic penta-2D materials in nanoelectronics and energy devices.