Abstract
We report on the calculation of phase transition in the configurational state (i.e. atomic arrangement) of Au
x
Cu
1−x
nanoparticle (or nano-alloy). The cluster expansion, represented by the formation energies of several atomic configurations, has been determined from full potential, linearized augmented-plane-wave first-principle calculation. The cluster expansion was then used as a Hamiltonian for the Monte-Carlo calculation of the phase transition between the configurational ground states (gs). Clear observation of plateau structures, associated with the calculated 'gs', in the plane of the composition (x) versus the chemical potential, have been observed at low temperatures <100 K. The plateaus smeared out at higher temperatures, giving rise to the order-disorder transition as the temperature rises. The critical temperature for this transition was estimated at 100 K, agreeing with the reported trend of the transition temperature with the nano-alloy size. Our results are thus relevant to applications concerning deposition of dispersed (i.e. well separated) nano-alloys.