First‐principles Study of Ca‐Alloying Effect on the Electronic, Structural, and Optical Response of MgH 2 ‐Based Metal Hydrides

ABSTRACT The electronic and optical properties of Mg 1 − x Ca x H 2 ( x = 0.00, 0.25, 0.50, 0.75, 1.00) metal hydrides are systematically investigated using first‐principles density functional theory to elucidate the role of Ca alloying. Pristine MgH 2 and CaH 2 are confirmed as wide‐band‐gap ionic insulators with metal–hydrogen bonding. Partial substitution of Mg by Ca introduces lattice distortions and electronic disorder, leading to band‐gap narrowing and the emergence of mid‐gap states. Projected density of states analysis reveals enhanced H(1s)–Ca(3p/4p) hybridization, promoting electronic delocalization and weakening metal–hydrogen interactions. Optical spectra exhibit pronounced red shifts and reduced peak intensities with increasing Ca content, reflecting enhanced polarizability and modified dielectric response. Intermediate compositions ( x ≈ 0.25 −0.50) show optimal electronic flexibility and optical performance, highlighting Ca alloying as an effective strategy for tailoring metal hydrides for hydrogen storage and energy applications.