  In order to improve the hydrogen storage properties of calcium hydride
(CaH2), we have tuned its thermodynamical properties through fluorination.
Using ab-initio total energy calculations based on density functional theory,
the structural stability, electronic structure and chemical bonding of CaH2-xFx
systems are investigated. The phase transition of fluorinated systems from
orthorhombic to cubic structure has been observed at 18% fluorine doped CaH2.
The phase stability analysis shows that CaH2-xFx systems are highly stable and
the stability is directly correlating with their ionicity. Density of states
(DOS) plot reveals that CaH2-xFx systems are insulators. Partial DOS and charge
density analyses conclude that these systems are governed by ionic bonding. Our
results show that H closer to F can be removed more easily than that far away
from F and this is due to disproportionation induced in the bonding interaction
by fluorination.
