Metropolis Monte Carlo predictions of free Co-Pt nanoclusters

The Metropolis Monte Carlo (MC) sampling method with a semi-empirical Embedded Atom Model (EAM) and a Modified EAM (MEAM) potentials is used to investigate structural properties of free Co-Pt nanoclusters. Sampling is achieved in the number-pressure-temperature (NPT) and the (Δμ-NPT) ensembles, where Δμ denotes the chemical potential difference between the Co and Pt subsystems. The model potentials are parameterised on the basis of the structure, the lattice distance, the vacancy formation energy, the bulk modulus and the cohesive energy of pure cobalt and platinum. The mixed repulsive contribution to the EAM configuration energy is here tuned in such a way to correctly predict the tetragonal ordered structure of CoPt at room temperature. MC predicts the ordered structure of Co₃Pt, CoPt and CoPt₃ phases as well as the order-disorder phase transition in CoPt. The results obtained with both potentials are compared. The study is then extended to isolated CoPt and Co₃Pt clusters containing a few hundred atoms and the consequences of temperature on predicted structural and segregation properties are investigated.