Ab initio electronic, dynamic, and thermodynamic properties of isotopic lithium hydrides (6LiH, 6LiD, 6LiT, 7LiH, 7LiD, and 7LiT)

The structural, dielectric, lattice-dynamical, and thermodynamical properties of isotopic lithium hydrides (6LiH, 6LiD, 6LiT, 7LiH, 7LiD, and 7LiT) were investigated within density-functional theory. The atomic structure was fully relaxed and the structural parameters were found to differ by less than 2% from the experimental data. The associated electronic band structure and density of states were also presented. A linear-response approach to the density-functional perturbation theory was employed to work out the Born effective charges, dielectric tensors and phonon frequencies, and thermodynamic properties. The compounds with the heavier Li isotope or H isotope have the lower phonon frequencies; 6LiT is more stable than 7LiT, 6LiD, 7LiD, 6LiH, and 7LiH in the temperature range 0–2700 K. These properties of LiT were predicted for the first time. The results were discussed in terms of the isotope effects on phonon dispersion curves and thermodynamic properties.