Density-functional calculations of α-Pu-Ga(Al) alloys

First-principles methods are employed to study the ground-state atomic volumes of α-Pu-Ga(Al) alloys. It is shown that a random distribution of Ga(Al) atoms in the monoclinic lattice of α-Pu results in a maximum expansion of this lattice and creation of the so-called α′-Pu phase. Any kind of ordering of Ga(Al) atoms on the monoclinic lattice results in a shrinking of the lattice constant while the ordered α8-(Pu-Ga(Al)) configuration yields the smallest lattice constant which is very close to that of pure α-Pu. In addition, energetics of the ordered (unrelaxed and relaxed) and disordered configurations is discussed.