Structure and energetics of Cu-Au alloys

The structures and energetics of Cu-Au alloys over a wide range of temperat ures are studied using a combination of quasi-harmonic (QH) lattice dynamic s and Monte Carlo (MC) simulations at constant temperature and constant pre ssure. The many-body potential used is fitted to room-temperature experimen tal data taking vibrational contributions into account. Transitions to the disordered phases are studied using MC simulations in which not only anisot ropic deformation of the unit cell and atomic movements are allowed, but al so exchange of atoms of different type is explicitly considered. Our calcul ations reproduce all characteristic features of the order-disorder transiti ons, including the characteristic peaks in the plots of heat capacity as a function of temperature.