MONTE-CARLO METHOD FOR SPIN MODELS WITH LONG-RANGE INTERACTIONS

We introduce a Monte Carlo method for the simulation of spin models wi th ferromagnetic long-range interactions in which the amount of time p er spin-flip operation is independent of the system size, in spite of the fact that the interactions between each spin and all other spins a re taken into account. We work out two algorithms for the q-state Pott s model and discuss the generalization to systems with other interacti ons and to O(n) models. We illustrate the method with a simulation of the mean-field Ising model, for which we have also analytically calcul ated the leading finite-size correction to the dimensionless amplitude ratio [m(2)](2)/[m(4)] at the critical temperature.