First-principles study of the anisotropic thermal expansion of hcp metals Be and Y

A first-principles study of the anisotropic thermal expansion of hcp metals Be and Y is reported. According to quasiharmonic approximation, the phonon spectra were computed at a set of lattice parameters using the pseudopotential plane wave method with the local density approximation in the framework of the density functional perturbation theory. The free energies were obtained according to the calculated phonon spectra and thermal properties such as specific heat at constant volume (pressure) were calculated. The electronic contribution to specific heat was found important to metal Y not only at very low temperature but also over room temperature. The calculated results are in good agreement with available experimental data in a wide range of temperature.