Phase stability and magnetism ofNi3Al

The structural phase stability of ${\mathrm{Ni}}_3$Al is investigated for its cubic (L$1_2$), tetragonal (D$0_{22}$), and hexagonal (D$0_{19}$) crystal structures with use of an all-electron total-energy local-density-functional approach. In agreement with experiment, the (weakly) ferromagnetic L$1_2$ structure is found to be the most stable phase. The calculated lattice constant (3.55 Å), the bulk modulus (2.1 Mbar), and the heat of formation (44.8 kcal/mol) are in fairly good agreement with experiment. The second-nearest-neighbor coupling between Ni d and Ni d states and the (higher-order) nearest-neighbor coupling between Ni d and Al p states may play an important role in accounting for the structural stability of ${\mathrm{Ni}}_3$Al. The inclusion of spin-orbit coupling is found to reduce the exchange-energy splitting and magnetic moment by ∼40%.