Nickel induced iono-covalent character of hydrogen in RbMgH3 from first principles

The large ionic character in hexagonal perovskite RbMgH3 is reduced by selective substitutions by Ni followed by full geometry optimization within DFT leading to preserve the structure and symmetry of the pristine hydride. From the Bader charge analysis, an increasingly iono-covalent character is introduced with larger amounts of Ni substituting to Mg. For the Ni rich composition RbMg1/3Ni2/3H3, found most stable from cohesive energies, the charge on H decreases down to −0.2. This peculiar behavior should enable enhancing the kinetics of H release for potential applications.