Prediction of the structural stability and superconducting properties of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>RbS</mml:mi> <mml:msub> <mml:mi mathvariant="normal">c</mml:mi> <mml:mn>2</mml:mn> </mml:msub> </mml

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 <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"> <a:mrow> <a:mi>RbS</a:mi> <a:msub> <a:mi mathvariant="normal">c</a:mi> <a:mn>2</a:mn> </a:msub> <a:msub> <a:mi mathvariant="normal">H</a:mi> <a:mi>x</a:mi> </a:msub> </a:mrow> </a:math> ternary system over pressures ranging from 150 to 300 GPa. Our results reveal that <d:math xmlns:d="http://www.w3.org/1998/Math/MathML"> <d:mrow> <d:mi>RbS</d:mi> <d:msub> <d:mi mathvariant="normal">c</d:mi> <d:mn>2</d:mn> </d:msub> <d:msub> <d:mi mathvariant="normal">H</d:mi> <d:mn>16</d:mn> </d:msub> </d:mrow> </d:math> adopts a highly symmetric cubic structure with space group <g:math xmlns:g="http://www.w3.org/1998/Math/MathML"> <g:mn>3</g:mn> <g:mi>m</g:mi> </g:math> , which is both dynamically and thermodynamically stable down to 150 GPa, featuring a hydrogen-based cage framework. Upon increasing hydrogen content, <h:math xmlns:h="http://www.w3.org/1998/Math/MathML"> <h:mrow> <h:mi>RbS</h:mi> <h:msub> <h:mi mathvariant="normal">c</h:mi> <h:mn>2</h:mn> </h:msub> <h:msub> <h:mi mathvariant="normal">H</h:mi> <h:mn>17</h:mn> </h:msub> </h:mrow> </h:math> 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- <k:math xmlns:k="http://www.w3.org/1998/Math/MathML"> <k:mn>3</k:mn> <k:mi>d</k:mi> </k:math> and H- <l:math xmlns:l="http://www.w3.org/1998/Math/MathML"> <l:mn>1</l:mn> <l:mi>s</l:mi> </l:math> 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 <m:math xmlns:m="http://www.w3.org/1998/Math/MathML"> <m:mrow> <m:mi>RbS</m:mi> <m:msub> <m:mi mathvariant="normal">c</m:mi> <m:mn>2</m:mn> </m:msub> <m:msub> <m:mi mathvariant="normal">H</m:mi> <m:mn>16</m:mn> </m:msub> </m:mrow> </m:math> at 150 GPa and 190.7 K for <p:math xmlns:p="http://www.w3.org/1998/Math/MathML"> <p:mrow> <p:mi>RbS</p:mi> <p:msub> <p:mi mathvariant="normal">c</p:mi> <p:mn>2</p:mn> </p:msub> <p:msub> <p:mi mathvariant="normal">H</p:mi> <p:mn>17</p:mn> </p:msub> </p:mrow> </p:math> 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 <s:math xmlns:s="http://www.w3.org/1998/Math/MathML"> <s:mrow> <s:mi>RbS</s:mi> <s:msub> <s:mi mathvariant="normal">c</s:mi> <s:mn>2</s:mn> </s:msub> <s:msub> <s:mi mathvariant="normal">H</s:mi> <s:mi>x</s:mi> </s:msub> </s:mrow> </s:math> system.