The formation energies of point defects, and the interaction energies of various defect pairs, were calculated from first principles within an order-N locally self-consistent Green's function method; together with multi-pole electrostatic corrections to the atomic-sphere approximation. The theory correctly reproduced the ground state for off-stoichiometric alloys. The constitutional defects (antisite Ni atoms and Ni vacancies in Ni-rich and Al-rich alloys, respectively) were shown to form ordered structures, in the ground state, in which they tended to avoid each other at the shortest distance on their sub-lattice. The predominant thermal defects in Ni-rich and stoichiometric alloys were predicted to be triple defects. In Al-rich alloys, another type of thermal defect predominated; in which two Ni vacancies were replaced by one antisite Al atom. As a result, the vacancy concentration decreased with temperature in that region.

Constitutional and Thermal Point Defects in B2 NiAl. P.A.Korzhavyi, A.V.Ruban, A.Y.Lozovoi, Y.K.Vekilov, I.A.Abrikosov, B.Johansson: Physical Review B, 2000, 61[9], 6003-18