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Z. Naturforsch. 2013, 68b, 44 – 50
doi:10.5560/ZNB.2013-2282
Hydrogen Insertion Effects on the Electronic Structure of Equiatomic MgNi Traced by ab initio Calculations
Samir F. Matar1,2, Adel F. Al Alam3 and Naim Ouaini3
1 CNRS, ICMCB, UPR 9048, F-33600 Pessac, France
2 Université de Bordeaux, ICMCB, UPR 9048, F-33600 Pessac, France
3 Université Saint Esprit de Kaslik (USEK), OCM (Optimisation et Charactérisation des Matériaux), URA GREVE, CSR-USEK, Jounieh, Lebanon
Reprint requests to S. F. Matar. E-mail: matar@icmcb-bordeaux.cnrs.fr
Received October 18, 2012 / published online January 10, 2013
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.
Key words: Hydrogen, Equiatomic MgNi, Iono-covalent Character, Bader Charge, Chemical Bonding
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