  The cellular automaton model is used to simulate diffusion and aggregation
with dissociation of point particles in 2D. A continuous phase transition is
found that separates creation of compact aggregates and fractal ones. The
transition is the function of pair-interaction energy ($E_b$), type of
neighborhood and temperature $T$. Manifestations of the transition in real
physical systems are discussed.

Computational Physics;Statistical Mechanics;Cellular Automata and Lattice Gases