First-principles investigation of Rb2CaH4 and Cs-doped Rb2CaH4: Unveiling their potential for hydrogen storage through mechanical and optoelectronic properties

Abstract

This study uses the density functional theory (DFT) approach with GGA-PBE to assess the effect of substituting alkali metals in Rb2CaH4 and Cs-doped Rb2CaH4 on their hydrogen storage potential. To address the challenges associated with predicting accurate electronic properties in materials containing heavier elements such as cesium, spin-orbit coupling (SOC) effects have been incorporated into our calculations. The mechanical robustness of both Rb2CaH4 and Cs-doped Rb2CaH4, as demonstrated by their mechanical properties, highlights these materials as promising candidates due to their stability in hydrogen storage applications. Anisotropic factors show that all materials exhibit anisotropy, suggesting a directional dependency in their properties. The Pugh ratio indicates that Rb2CaH4 and Cs-doped Rb2CaH4 are brittle materials. Based on the calculated band gap, the electronic band structure analysis, conducted using both HSE06 and GGA-PBE, shows that Rb2CaH4 and Cs-doped Rb2CaH4 are wide-bandgap materials. Rb2CaH4 and Cs-doped Rb2CaH4 exhibit the highest optical conductivity, absorption coefficient, and energy loss function among optoelectronic materials, emphasizing their superior absorption and electron transfer capabilities. The hydrogen storage capacity has been evaluated for practical applications; Rb2CaH4 and Cs-doped Rb2CaH4 show the highest gravimetric and volumetric capacities.