Calculation of the electronic and structural properties of cubic Mg2NiH4

The electronic, structural, and stability properties of the cubic hydride Mg2NiH4 are analyzed based on ab initio total-energy calculations. We evaluate the electronic band structures, density of states, charge-density distributions, and bond character for different hydrogen configurations. The hydrogen distribution that minimizes the total energy corresponds to a tetrahedrally distorted square-planar coordination of the nickel atoms with a Ni-H bond length of 1.548 Angstrom, in good agreement with neutron-diffraction experimental data. The evaluation of the relative stabilities of Mg2NiH4 and other hypothetical compounds of composition Mg2NiHdelta (delta=0,2,4,6) agree with the observation that essentially stoichiometric Mg2NiH4 is the only phase present in the equilibrium phase diagram of the Mg-Ni-H system. [S0163-1829(99)13413-1].