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On the isotope effects of ZrX2 (X = H, D and T): A First-principles study

Zirconium hydride is an important material for storage of hydrogen isotopes. 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 in terms of the electronic density of states, charge density distribution and the electron localization function. The phonon dispersion curves, phonon density of states and thermodynamic properties of ZrX2 (X= H, D, T) compounds were evaluated based on frozen phonon method. Both the Raman and infrared active vibrational modes of ZrX2 at Γ-point were analyzed which showed significant isotopic effect on ZrX2 compounds. For example, the 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 -113.97, -126.50 and -132.04 kJ/(mole of compound) for X = H, D and T, respectively.