Theoretical Investigation of Grain-Boundary Engineering for Thermal Transport Control in Janus 2D Transition Metal Dichalcogenides: Implications for Nanoscale Thermal Management

The influence of mirror-twin grain boundaries (GBs) on phonon transport in Janus two-dimensional transition-metal dichalcogenides is investigated using neuroevolution-potential (NEP)-based nonequilibrium molecular dynamics (NEMD) simulations. The primary comparison is made among P 3 m 1-type Janus PtSSe and ZrSSe, authentic P 3 m 1 WSSe, and an idealized planar WSSe reference constructed to preserve WS 2 -like interfacial registry. The P 3 m 1 GBs show strong thermal-transport suppression, whereas the planar WSSe reference retains much higher phonon transmission. Structural, bonding, local projected VDOS, and spectral heat-current analyses indicate that the strong suppression in the P 3 m 1 systems is associated with out-of-plane registry mismatch and enhanced low-frequency interfacial vibrational perturbation. The results are framed as a controlled theoretical study of symmetry-related interfacial phonon scattering in idealized Janus mirror-twin boundary models, with implications for nanoscale thermal management.