First-principles phonon calculations on the lattice dynamics and thermodynamics of rare-earth intermetallics TbCu and TbZn

The structural, lattice dynamical, and thermodynamical properties of rare-earth intermetallics TbZn and TbCu with CsCl-type structure have been investigated by performing the first principles calculations, in which the density-functional theory (DFT) and density-functional perturbation theory (DFPT) have been employed within the plane-wave basis projector augmented wave (PAW) method. The quasiharmonic approximation (QHA) has been used to estimate the free energies. The phonon frequencies, thermal expansion coefficients, heat capacities, and the elastic moduli at finite temperature are presented. The calculated results for the benchmark metal Cu are in better agreement with the experimental data in comparison with the previous DFT results. Both the elastic moduli and the phonon-dispersion curves demonstrate that the anisotropy of TbZn is larger than that of TbCu. The thermal expansion coefficient of TbZn as a function of temperature is larger than that of TbCu.