Ambient pressure phase diagram of plutonium: A unified theory for alpha-Puand delta-Pu

We present a general theoretical approach that successfully describes the a nomalous delta phase of plutonium, while at the same time being generally a pplicable for any metal, including alpha -Pu. For this purpose, we have use d density-functional theory expanded to include additional electron correla tion effects by means of gradient density corrections and spin/orbital pola rization. Within this scheme, equilibrium volume, bulk modulus, and total e nergy of alpha -Pu and delta -Pu are calculated accurately without invoking ad hoc treatments or semi-empirical models for either phase. These anomalo us properties of the delta 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 delta phase are consistent with experiments.