Crystal feature and electronic structure of novel mixed alanate LiCa(AlH4)3: a density functional theory investigation

The crystal structure of LiCa(AlH4)(3) was investigated via first principle calculations, especially the positions of hydrogen atoms undetected in XRD experiments were predicted, then the thermodynamic favourability of the experimentally reported structure with respect to several candidates from the inorganic crystal structure database (ICSD) was confirmed. It is found that hexagonal packing of AlH4 layers along the c axis is present in LiCa(AlH4)(3), and the detailed geometrical feature is further revealed. The electronic structures show that in LiCa(AlH4)(3) the Li-AlH4 interaction is more covalent than in LiAlH4, while the Ca-AlH4 covalence is less than in Ca(AlH4)(2). The overall stronger covalence in LiCa(AlH4)(3) leads to weakened Al-H bonds. The Li-H interaction in LiCa(AlH4)(3) dramatically turns out to be strong bonding, opposite to the Li-H anti-bonding in LiAlH4. The Ca-H bonds are more anti-bonding in LiCa(AlH4)(3).