Thermal evolution of vibrational properties ofα-U

Abstract

By means of ab initio molecular dynamics calculations, the thermal evolution of vibrational properties in $\ensuremath{\alpha}$-U is studied at low temperature. The phase transition undergone by this material around 50 K was previously studied extensively using ab initio calculations in the framework of the linear response at 0 K. Although these previous efforts capture successfully the complexity of the experimental phonon spectrum at room temperature, in particular the soft-phonon mode and its pressure dependence, they fail to reproduce the transition to the charge-density-wave state at ambient pressure as a function of temperature. In the present work, by going beyond the quasiharmonic approximation and taking into account the temperature effects explicitly, we are able to reproduce the behavior of both phonon spectrum and elastic constants of U-$\ensuremath{\alpha}$ as a function of temperature.