Kawasaki dynamics and equilibrium distributions in simulations of phase separating systems

We compare equilibrium probability distributions obtained from Monte Carlo simulations for different spin exchange dynamics with the exact Boltzmann distribution for the fixed magnetization Ising model on small lattices. We present simple arguments and numerical evidence in order to show that "efficient" Kawasaki exchange does not lead to Boltzmann equilibrium distributions and that nearest-neighbour equal spin-exchange must be considered. Arbitrary distance opposite spin interchange is indicated as an alternative to obtaining the full phase diagram with phase separation.