Prediction of the structural stability and superconducting properties of RbS c 2 hydrides under high pressure

Ternary hydrides, owing to their chemical diversity and structural tunability, are considered important candidate systems for the exploration of high-temperature superconductivity. In this work, we performed systematic structure searches and superconductivity calculations on the RbS c 2 H x ternary system over pressures ranging from 150 to 300 GPa. Our results reveal that RbS c 2 H 16 adopts a highly symmetric cubic structure with space group 3 m , which is both dynamically and thermodynamically stable down to 150 GPa, featuring a hydrogen-based cage framework. Upon increasing hydrogen content, RbS c 2 H 17 forms a fully occupied cage structure with enhanced H-H interactions and strengthened Sc-H hybridization. Electron localization function, crystal orbital Hamilton population, and Bader charge analysis collectively indicate that the bonding is dominated by strong H-H covalent interactions, supported by ionic contributions from Sc-H bonds. Electronic structure calculations show pronounced metallicity with Sc- 3 d and H- 1 s hybridization dominating near the Fermi level, facilitating strong electron-phonon coupling. The superconducting critical temperatures estimated using the Allen-Dynes modified McMillan formula reach 140 K for RbS c 2 H 16 at 150 GPa and 190.7 K for RbS c 2 H 17 at 200 GPa, underscoring the crucial role of hydrogen occupancy in optimizing superconducting behavior. The results indicate that variations in hydrogen content have a noticeable effect on the stability and superconducting characteristics of the RbS c 2 H x system.