Breakdown of nucleation theory for crystals with strongly anisotropic interactions between molecules

We study the nucleation of model two-dimensional crystals in order to gain insight into the effect of anisotropic interactions between molecules on the stationary nucleation rate J. With the aid of kinetic Monte Carlo simulations, we determine J as a function of the supersaturation s. It turns out that with increasing degree of interaction anisotropy the dependence of ln J on s becomes step-like, with jumps at certain s values. We show that this J(s) dependence cannot be described by the classical and atomistic nucleation theories. A formula that predicts the identified J(s) behavior is yet to be derived and verified, and the present study provides the necessary data and understanding for doing that.