Structure, chemical ordering and thermal stability of Pt-Ni alloy nanoclusters.

Equilibrium structures, chemical ordering and thermal properties of Pt-Ni nanoalloys are investigated by using basin hopping-based global optimization, Monte Carlo (MC) and molecular dynamics (MD) methods, based on the second-moment approximation of the tight-binding potentials (TB-SMA). The TB-SMA potential parameters for Pt-Ni nanoalloys are fitted to reproduce the results of density functional theory calculations for small clusters. The chemical ordering in cuboctahedral (CO) Pt-Ni nanoalloys with 561 and 923 atoms is obtained from the so called semi-grand-canonical ensemble MC simulation at 100 K. Two ordered phases of L12 (PtNi3) and L10 (PtNi) are found for the CO561 and CO923 Pt-Ni nanoalloys, which is in good agreement with the experimental phase diagram of the Pt-Ni bulk alloy. In addition, the order-disorder transition and thermal properties of these nanoalloys are studied by using MC and MD methods, respectively. It is shown that the typical perfect L10 PtNi structure is relatively stable, showing high order-disorder transition temperature and melting point among these CO561 and CO923 Pt-Ni nanoalloys.