We investigated the electronic structure of the RNiSn (R=La,Ce,Pr,Nd) intermetallic compounds as well as their corresponding mono- and dihydrides. We computed the energy bands and the total and partial densities of states using a mixed approach; a pseudopotential scheme and ab initio full potential-all electron band-structure techniques. The crystal structure was investigated for each of the 12 compounds by performing full geometry optimization. We determine the magnetic properties of these compounds. We also analyze the details of the bonding in these systems, in particular, the effect of the hydrogen insertion in the parent intermetallic compounds. We found that, besides the nonmagnetic reference systems LaNiSnH_x, the Pr- and Nd-derived systems are consistent with f~(+2) and f~(+3) electronic configurations. The case of the Ce compounds, as expected, showed a more complicated situation; the computed magnetic moment suggests an intermediate valence state for CeNiSnH. The decomposition enthalpies for the mono- and dihydrides have been estimated and compared with experimental values for similar compounds.
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