Constant temperature and pressure monte carlo study of the order-disorder transition of Cu3Au

Abstract

An N-body potential is found for the intermetallic CusAu and is tested for both the static and dynamic properties. This potential is a better approximation than the pair potentials and can be used for the description of defects and the relaxation effects on the order-disorder transition. It is the first time that such a potential can reproduce the dynamical properties of a first-order phase transition. Although the transition temperature is lower than the experimental findings by 25%, it is found that many of the macroscopic properties change at the critical point in a steplike fashion and have, compared to known experimental data, the correct discontinuity. This is quite remarkable since all the parameters have been determined at T = 0 K. Also the chemical potential difference between Cu and Au is determined for the stoichiometry of Cu3Au. This quantity is continuous at the transition temperature and shows a discontinuity in its slope.

Cu-Au, Ag-Au, Cu-Ag, and Ni-Au intermetallics: First-principles study of temperature-composition phase diagrams and structures

“…Most notably, this system has been considered as the basic test case for the classic Ising-hamiltonian statistical-mechanics treatment of alloys. [25][26][27][28][29][30][31][32] More recently, noble metal binary alloys have been treated theoretically via empirical fitting of the constants in Ising hamiltonians, [25][26][27][28][29][30][31][32][33][34] semiempirical interatomic potentials, [35][36][37][38][39][40][41][42][43][44][45][46][47] and via first-principles cluster expansions. [48][49][50][51][52][53][54][55] The essential difference in philosophy between the classical application of Ising models to CuAu [25][26][27][28][29][30]33 and more modern approaches based on the density functional formalism 64 i...…”

Monte Carlo study of the [001] surface ofCu3AuforT≠0K

“…For example, examining the stoichiometry profile and the order parameter, it can be observed that all layers independently reach a common value for the bulk part, apart from the expected fluctuations. Furthermore, the chemical potential was obtained by performing calculations 20,21 in the bulk, independent of the present simulations. By comparing the bulk part of the simulation cell with the bulk simulations mentioned above, it can be noted that for different properties the same values are obtained.…”

“…This chemical potential difference is determined from the bulk by doing a series of simulations. 20,21 The accuracy of the Monte Carlo method depends strongly on the number of configurations sampled. A Monte Carlo step comprises of a number of attempts, which is equal to the number of atoms in the system, to move and mute atoms randomly chosen.…”

“…The values for the chemical potential difference were gained from our analysis of the bulk order-disorder transition. 20,21 In Fig. 1 we depict the stoichiometry profile of Cu 3 Au along the ͓001͔ direction for T/T c ϭ0.8 ͑circles͒ and 0.9 ͑rhombuses͒.…”

Thermodynamical properties and defect energetics of an n-body potential adapted to Cu3Au

“…Moreover, comparison with experimental data can be made by scaling quantities of interest with Tc as shown by recent work [38].…”