a final temperature $T_f<T_0$ we start with a random distribution of atoms at time $t=0$ and let the system evolve in time at $T_f$. The ensuing equilibration process is analyzed by calculating energies, structure factors, and other ordering characteristics from averages over 10 independent Monte Carlo runs.

As the first application of our atom–vacancy exchange algorithm we have calculated tracer diffusion coefficients for $A$– and $B$–atoms in the disordered phase close to $T_0$. Since in our model $V_{AA}=V_{AB}$, the jump of an $A$–atom will leave the interaction energy with its environment almost unchanged and hence $D_A$ is found to be nearly temperature–independent. The $BB$–repulsion, on the other hand, gives rise to a temperature-dependent $D_B<D_A$, see the inset of Fig. 1. As these results refer to a fixed vacancy concentration, they cannot be directly related to experiments, where $c^V(T)$ normally is a strong function of $T$.[@vacancy] Nevertheless, the ratio $D_A/D_B \simeq 2$ at $T/T_0=1.7$ very roughly agrees with the experimental value $D_{Cu}/D_{Au} \simeq 1.45$ for Cu$_3$Au at the same $T/T_0$–ratio,[@diffusion] thus supporting our choice of nearest–neighbor interaction parameters. Moreover, in an attempt to map the Monte Carlo time to the physical time scale, we can exploit experimental knowledge of $c^V(T)$ for 