CROSSOVER SCALING IN 2 DIMENSIONS

We determine the scaling functions describing the crossover from Ising -like critical behavior to classical critical behavior in two-dimensio nal systems with a variable interaction range. Since this crossover sp ans several decades in the reduced temperature as well as in the finit e-size crossover variable, it has up to now largely evaded a satisfact ory numerical determination. Using a dedicated Monte Carlo method, we could obtain accurate results for sufficiently large interaction range s. Our data cover the full crossover region both above and below the c ritical temperature and support the hypothesis that the crossover func tions are universal. Also the so-called effective exponents are discus sed and we show that these can vary nonmonotonically in the crossover region.