First Principles and MonteCarlo Simulation forInvestigation of PhaseTransition in Au1-xCux Nano Alloys

Abstract

The calculation of phase transition in the configurational state (i.e. atomic arrangement) of AuxCu1-x nanoparticle (or Nano alloy)have been investigated by first principles and Monte Carlo calculations. The cluster expansion represented by the formation energies of several atomic configurations have 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 transitions with temperature. The critical temperature for this transition was estimated at 100 K, consistent with the reported trend of the transition temperature with the Nano alloy size. Our results are thus relevant to applications concerning deposition of dispersed Nano alloys at small size ~ 10 atoms per Nano alloy.All the Nano-alloys structures were geometrically optimized before executing the above-mentioned calculations. The geometrical optimization involved the calculation of the mechanical properties of Nano alloys where we performed atomistic simulations to study the structure and Elastic constants for Au-Cu Nano-Alloy. Approaches used to compute the bulk modulus and lattice constant, one based on a definition in terms of the lattice parameter derivative of the total energy and another in terms of the volume derivative of the pressure often used in simulations. Both give quantitatively similar results.