Light elements-induced iono-covalent character in MgH2: An ab-initio approach

The overall large ionic character of MgH2 is reduced by inserting light elements from the first period, B and C, using a trirutile host superstructure. From DFT computations, both elements are found destabilizing to the structure with largely positive cohesive energy with interstitial B and slightly negative cohesive energy with interstitial C. This trend is also observed for low amounts of insertion down to (B,C)0.167MgH2. From the Bader charge analysis the largely ionic character of hydrogen is decreased to an average H−0.37 in the neighborhood of C and H−0.75 for the other hydrogen atoms (resp. H−0.64 and H−0.76 for B insertion). This peculiar behavior should enable enhancing the kinetics of H release for potential applications.