On the applicability of the classical nucleation theory in an Ising system

Large-scale dynamic Monte Carlo simulations of a lattice gas on a 2000x2000 square lattice with a Glauber-type spin flip dynamics were performed. The results are discussed in the light of classical nucleation theory (CNT) whi ch can be fully specified for the problem due to the availability of exact values for the interfacial energy of a large nucleus, known from the Onsage r solution. Several alternative (field-theoretic or nonclassical) descripti ons were also considered. Special attention was paid to the pre-exponential in the cluster distribution function and to the finite-size corrections to the interfacial energies which are required in order to comply with observ ations. If taken literally, the CNT produces large errors when predicting e ither the cluster distribution function or the nucleation rate. However, at intermediate temperatures (up to 0.7 T-c) the correspondence can be substa ntially improved by considering the low-temperature properties of small clu sters and adjusting the pre-exponential. At higher temperatures the CNT is in qualitative disagreement with the simulations. Several explanations for this, including coagulation between clusters, are proposed. (C) 1999 Americ an Institute of Physics. [S0021-9606(99)51638-3].