A DFT study to investigate physical properties and hydrogen storage capability of Mn-based hydride perovskites XMnH3 (X = Ba, Ca) for hydrogen storage application

The present study investigates the physical properties of XMnH3 (X = Ba, Ca) using a DFT approach to explain their abilities for hydrogen storage application. The calculated lattice parameters were found 4.06 and 3.67 angstrom for BaMnH3 and CaMnH3, respectively. Both the compounds are found indirect band gap semiconductor materials as investigated with the help of band structure and density of states. The value of band gap is found 2.55 and 3.01 eV for BaMnH3 and CaMnH3, respectively. The magnetic properties show that both materials possess antiferromagnetic nature. The optical properties including dielectric function, reflectivity, absorption, refractive index, conductivity, and loss function are also investigated in detail. Both materials are found mechanically stable, anisotropic, brittle, and hard. The Poisson's ratio predicts the covalent bonding in BaMnH3, and ionic bonding in CaMnH3. The gravimetric hydrogen storage capacity is found as 1.55 % and 3.09 % for BaMnH3, and CaMnH3, respectively, which shows that both materials are capable of storing hydrogen, however, CaMnH3 is suggested as a preferred material for hydrogen storage application.