Phonon-based Mechanisms for Structural Transformations in Pu

Plutonium undergoes a number of transformations that involve changes in unit cell shape and numbers of atoms. We focus on the fcc to monoclinic $\delta \rightarrow \alpha^{\prime}$ transformation and suggest displacive mechanisms that can describe the transformation. We also explore signatures of the mechanisms in phonon dispersion curves and present a phase diagram in paramter space. The implications for the $\beta \rightarrow \alpha$ transformation, assuming a displacive mechanism, will also be explored.