Phase stability and magnetism of Ni3Al

The structural phase stability of Ni3Al is investigated for its cubic (L12), tetragonal (D022), and hexagonal (D019) crystal structures with use of an all-electron total-energy local-density-functional approach. In agreement with experiment, the (weakly) ferromagnetic L12 structure is found to be the most stable phase. The calculated lattice constant (3.55), 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 Ni3Al. The inclusion of spin-orbit coupling is found to reduce the exchange-energy splitting and magnetic moment by 40%.