Ambient pressure phase diagram of plutonium: A unified theory for α-Pu and δ-Pu

We present a general theoretical approach that successfully describes the anomalous δ phase of plutonium, while at the same time being generally applicable for any metal, including α-Pu. For this purpose, we have used density-functional theory expanded to include additional electron correlation effects by means of gradient density corrections and spin/orbital polarization. Within this scheme, equilibrium volume, bulk modulus, and total energy of α-Pu and δ-Pu are calculated accurately without invoking ad hoc treatments or semi-empirical models for either phase. These anomalous properties of the δ phase are shown to be a consequence of magnetism. However, spin and orbital moment are close in magnitude and antiparallel, so that the total moment nearly vanishes. Calculated elastic constants and electronic structure of the δ phase are consistent with experiments.