Alkaline-earth substitution effects on the physical properties and hydrogen-storage performance of cubic MSc₃H₈ (M =...

First-principles calculations were employed to investigate the effect of alkaline-earth substitution on the physical properties and hydrogen-storage performance of cubic MSc₃H₈ (M = Ba, Ca, Sr) hydrides. All three compounds exhibit negative formation energies relative to the selected elemental reference states and satisfy the mechanical-stability criteria. Their calculated elastic indicators suggest a predominantly brittle response, with CaSc₃H₈ exhibiting the highest overall stiffness and BaSc₃H₈ the lowest elastic anisotropy. The electronic structures are metallic, with Sc-3d states dominating near the Fermi level and appreciable Sc-3d/H-1s hybridization in the valence region. Phonon calculations indicate local harmonic dynamical stability of the optimized cubic phases at 0 K. Among the investigated compounds, CaSc3H8 exhibits both the highest gravimetric hydrogen capacity (4.41 wt%) and the highest volumetric hydrogen density (112.80 g H₂ L^-1), whereas BaSc₃H₈ has the lowest estimated desorption temperature 340 K, indicating comparatively easier hydrogen release within the simplified thermodynamic model adopted in this work.

Density functional theory calculations were performed using the Quantum ESPRESSO package with the PBE generalized-gradient approximation and PAW pseudopotentials. Plane-wave kinetic-energy cutoffs of 60 Ry and 600 Ry were used for the wave functions and charge density, respectively, together with an 8×8×8 k-point mesh. Lattice-dynamical properties were evaluated within density-functional perturbation theory using a 4×4×4 q-point mesh, while phonon densities of states were obtained using an 8×8×8 q-point mesh. Vibrational thermodynamic properties were evaluated using the thermo_pw package.