First principles study of the ZrX2 (X = H, D and T) compounds

The Zr–H system is of particular importance for the solid state storage of hydrogen isotopes in the form of zirconium hydride. Here we report the structural, electronic, vibrational and thermodynamic properties of ZrH2, ZrD2 and ZrT2 using density functional theory (DFT). The structural optimization was carried out by the plane-wave based pseudo-potential method under the generalized gradient approximation (GGA) scheme. The electronic structure of the ZrH2 compound was illustrated explicitly. The vibrational, thermodynamic, and the effect of isotopes on ZrX2 (X = H, D, T) compounds were evaluated by the frozen phonon method. Both the Raman and infrared active vibrational modes of ZrX2 at Γ-point showed significant isotopic effect on ZrX2 compounds. For example, the phonon energy gap between optical and acoustic modes reduces for ZrT2 than ZrD2 and ZrH2. The formation energies of ZrX2 compounds, including the ZPE contributions, were estimated to be −143.68, −147.87 and −150.01 kJ/(mole of compound) for X = H, D and T, respectively.