Collective diffusion in a two-dimensional lattice-gas system undergoing first-order phase transition was studied both theoretically and by means of Monte Carlo simulations. The nearest-neighbor attractive interactions result in the formation of a two-phase mixture in which the characteristic size of the dense phase grows with time as t1/3. It was shown analytically that the evolution of large-scale coverage inhomogeneities was governed by the diffusion equation with a negative diffusion coefficient. Similar to the phenomenon of Ostwald ripening, the Gibbs-Thompson effect was responsible for this abnormal diffusion. Monte Carlo simulations of random jumps of individual particles also showed the presence of negative diffusion caused by the macroscopically inhomogeneous distribution of particle density. The collective diffusion coefficients obtained both theoretically and by means of Monte Carlo simulations were in satisfactory agreement.

Negative Diffusion Coefficient in a Two-Dimensional Lattice-Gas System with Attractive Nearest-Neighbor Interactions. P.Argyrakis, A.A.Chumak, M.Maragakis, N.Tsakiris: Physical Review B, 2009, 80[10], 104203