Based on first-principle calculations1, we have systematically explored the nature of the elastic stability and the delta-delta'-epsilon phase transitions in pure Pu at high temperature. It is found that, both the electron-phonon coupling and the spin fluctuation effects tend to decrease the tetragonal elastic constant (C') of delta-Pu, accounting for its anomalous softening at high temperature. The lattice thermal expansion together with the electron-phonon coupling can stiffen C' of epsilon-Pu, promoting its mechanical stability at high temperature. The delta-epsilon transition is calculated to take place around 750-800 K, and is dominated by the phonon vibration. The delta' intermediate phase is realized around 750 K mainly because of the thermal spin fluctuation.
1) Li, C-M ; Johansson, B and Vitos, L SCIENTIFIC REPORTS 7, Article Number: 5632, (2017)