New Pseudo-Phase Structure for $α$-Pu

Abstract

In this paper we propose a new pseudo-phase crystal structure, based on an orthorhombic distortion of the diamond structure, for the ground-state $α$-phase of plutonium. Electronic-structure calculations in the generalized-gradient approximation give approximately the same total energy for the two structures. Interestingly, our new pseudo-phase structure is the same as the Pu $γ$-phase structure except with very different b/a and c/a ratios. We show how the contraction relative to the $γ$ phase, principally in the $z$ direction, leads to an $α$-like structure in the [0,1,1] plane. This is an important link between two complex structures of plutonium and opens new possibilities for exploring the very rich phase diagram of Pu through theoretical calculations.