Monte Carlo study of the [001] surface of Cu 3 Au for T ≠ 0 K

Using an N-body potential with parameters determined from the $T=0$ K bulk properties (lattice constant, cohesive energy, and the elastic properties) of Cu, Au, and ${\mathrm{Cu}}_{3}\mathrm{Au},$ we investigate the effect of the [001] surface of ${\mathrm{Cu}}_{3}\mathrm{Au}$ on the ordering for temperatures below and above the bulk order-disorder transition temperature, utilizing the constant pressure, temperature and chemical potential difference Monte Carlo method. The properties studied include the stoichiometry profile, the structure factor, the average position of the atoms along the [001] direction, short-range order, wetting phenomena, and mean-square displacements. Also, various instantaneous atomic configurations are plotted. Our interest is focused on the study of the segregation of Au to the surface, while the atoms are free to relax. We find that the surface affects the ordering of the layers close to it. Segregation is found to occur in agreement with experimental results. Oscillatory segregation appeared in our results only for the case where the atoms were not allowed to relax, and in a lower intensity in some off-stoichiometry cases, i.e., ${\mathrm{Cu}}_{0.7}{\mathrm{Au}}_{0.3}$ and ${\mathrm{Cu}}_{0.8}{\mathrm{Au}}_{0.2}.$