Hydrogen insertion effects on the electronic structure of equiatomic MgNi traced by ab initio calculations

Samir F. Matar (1) , Adel F. Al Alam (2) , Naïm Ouaïni (2)

1 ICMCB - Institut de Chimie de la Matière Condensée de Bordeaux
2 Faculté des Sciences et de Génie Informatique

For equiatomic MgNi which can be hydrogenated up to the composition MgNiH1.6 at an absorption/desorption temperature of 200 °C, the effects of hydrogen absorption are approached with the model structures MgNiH, MgNiH2 and MgNiH3. From full geometry optimization and calculated cohesive energies obtained within DFT, the MgNiH2 composition close to the experimental limit is identified as most stable. Charge density analysis shows an increasingly covalent character of hydrogen: MgNiH (H−0.67) → MgNiH2 (H−0.63) → MgNiH3 (H−0.55). While Mg-Ni bonding prevails in MgNi and hydrogenated model phases, extra itinerant low-energy Ni states appear when hydrogen is introduced signaling Ni-H bonding which prevails over Mg-H as evidenced from total energy calculations and chemical bonding analyses.

Keywords: Hydrogen; Equiatomic MgNi; Iono-covalent character; Bader charge; Chemical bonding

Domains: Material chemistry

Samir F. Matar, Adel F. Al Alam, Naïm Ouaïni. Hydrogen insertion effects on the electronic structure of equiatomic MgNi traced by ab initio calculations. Zeitschrift fur Naturforschung B, 2013, 68 (1), pp.44-50. ⟨10.5560/ZNB.2013-2282⟩. ⟨hal-00776491⟩