Nonphysical thermodynamical phases in L12 intermetallic alloys from semiempirical tight-binding potentials

We have calculated energies of antiphase boundaries (APB) and stacking faults for the face-centered cubic L12 structured Ni3Al, Cu3Au, and Au3Cu compounds. The calculations were performed using widely employed semiempirical potentials, which are derived from the second-moment approximation of a tight-binding model, and adopting different parameterizations for these potentials found in the literature. Our calculations show that the energies of all the APB’s on the (0 0 1) plane are lower than that of the L12 ordered alloy. In addition, we performed metropolis Monte Carlo simulations allowing the interchange of atoms and verified that the system chooses spurious low energy APB configurations. These results indicate that the thermodynamically stable phase obtained using these potentials is not the experimentally verified L12 phase at low temperatures. This is a relevant result because in all situations where ordering is allowed to change, the physical description using these potentials is expected to fail.