Temperature-Dependent Dynamical Stability and Diffusion in Hydrogen-Substituted Derivatives of Parent Janus WS ₂ van der Waals Monolayer

We propose a novel phase of hydrogen-substituted Janus WS2 using a cluster expansion approach based on the density functional theory (DFT). This method reveals that W3SH5 is an energetically stable structure adopting a hexagonal lattice. Going beyond the zero-Kelvin limitation of conventional DFT, we demonstrate that the W3SH5 phase remains dynamically stable up to 300 K, as confirmed by temperature-dependent effective potential calculations. Shedding light on the electronic properties, spin–orbit coupling (SOC) has a significant effect on the electronic structure by lifting band degeneracies, resulting in an increased density of states at the Fermi level. Moreover, the inclusion of SOC in W3SH5 elucidates the contribution of H orbitals, which show a pronounced accumulation near the Fermi level. Regarding hydrogen diffusion, we determined the most favorable pathways through total energy calculations. The results suggest that hydrogen atoms preferentially diffuse through subsurface channels rather than along the top of the W–S layer, indicating that off-layer diffusion is energetically more favorable.