Ab-Initio Study Of High Temperature Lattice Dynamics Of Bcc Zirconium (Beta-Zr) And Uranium (Gamma-U)

Using self consistent ab-initio lattice dynamics calculations, we show that bcc structures of Zr and U phases become stable at high temperature by phonon-phonon interactions. The calculated temperature dependent phonon dispersion curve (PDC) of beta-Zr match excellently with experimental PDC. But the calculated PDC for gamma-U shows negative phonon frequencies even at solid to liquid transition temperature. We show that this discrepancy is due to an overestimation of instability depth of bcc U phase which is removed by incorporation of spin-orbit coupling in the electronic structure calculations.