Hydrogen storage potential and physical properties of XSiH3 (X = Bi, Ga) Perovskite hydrides: A first-principles study

In this study, we present a comprehensive first-principles investigation of the structural, electronic, optical, thermodynamic, and hydrogen storage properties of cubic perovskite-type hydrides XSiH${}_3$ (X = Bi, Ga) within density functional theory using the full-potential linearized augmented plane wave method, as implemented in WIEN2k. Our structural optimization confirms that both BiSiH${}_3$ and GaSiH${}_3$ crystallize in a stable cubic structure (space group Pm$\bar{3}$m). Electronic band structure and density of states calculations confirm the metallic nature of both compounds, with the intersection of the valence and conduction bands at the Fermi level. Optical calculations reveal strong absorption in the visible and ultraviolet spectral regions, with GaSiH${}_3$ exhibiting strong plasmonic behavior. Thermodynamic calculations using the quasi-harmonic Debye model confirm their thermal robustness under varying pressures, with GaSiH${}_3$ showing higher entropy and Debye temperature values. Furthermore, hydrogen storage calculations confirm that GaSiH${}_3$ has a higher gravimetric capacity (3.00 wt%) compared to BiSiH${}_3$ (1.26 wt%) and releases hydrogen at a moderately elevated temperature, suggesting its greater suitability for hydrogen storage. However, decomposition energy calculations indicate that partial structural degradation may occur during hydrogen desorption, potentially limiting the reversibility of hydrogen uptake. Additionally, ab initio molecular dynamics simulations demonstrate that both BiSiH${}_3$ and GaSiH${}_3$ maintain their structural integrity with only minor thermal fluctuations in total energy, further confirming their dynamical stability. This theoretical analysis provides predictive insight into the multifunctionality of XSiH${}_3$ hydrides, which may guide future experimental efforts in energy and optoelectronic device applications.