MEDIUM-RANGE INTERACTIONS AND CROSSOVER TO CLASSICAL CRITICAL-BEHAVIOR

We study the crossover from Ising-like to classical critical behavior as a function of the range R of interactions. The power-law dependence on R of several critical amplitudes is calculated from renormalizatio n theory. The results confirm the predictions of Mon and Binder, which were obtained from phenomenological scaling arguments. In addition, w e calculate the range dependence of several corrections to scaling. We have tested the results in Monte Carlo simulations of two-dimensional systems with an extended range of interaction. An efficient Monte Car lo algorithm enabled us to carry out simulations for sufficiently Larg e values of R, so that the theoretical predictions could actually be o bserved.