STRUCTURAL-PROPERTIES OF PLUTONIUM FROM FIRST-PRINCIPLES THEORY

First-principles theory is shown to account for the unique low-tempera ture crystal structure of plutonium metal (alpha-PU). Also the observe d, and debated, upturn of the equilibrium volume between neptunium and plutonium is reproduced and found to be a consequence of the differen t crystal structures for these two metals. Thus it is shown that densi ty-functional theory is able to accurately describe bonding properties of 5f electrons in an outstandingly complex system, where also relati vistic effects are large. The electronic structure for alpha-Pu and fo r plutonium in competing close-packed crystal structures are also pres ented. Moreover, an explanation for the occurrence of the highly compl ex alpha-Pu structure is given. The mechanism is described in terms of a Peierls distortion in conjunction with a narrow 5f-band width. The energy gained from the splitting of the 5f bands outweighs the electro static energy which favors the high symmetry structures found for most other metals. At lower volumes we predict that plutonium should becom e bcc.