Microscopic model of diffusion limited aggregation and electrodeposition in the presence of leveling molecules.

We present a cellular automata approach for microscopic modeling of the effect of unbinding in diffusion limited aggregation. The automata represent active particles, which are able to change their internal state and affect their neighbors. The geometry resembles electrochemical deposition-"ions" diffuse at random from the top of a container until encountering an aggregate in contact with the bottom, to which they stick. This model exhibits dendritic (fractal) growth in the diffusion limited case. The addition of a field eliminates the fractal nature but the density remains low. The addition of molecules that unbind atoms from the aggregate transforms the deposit to a 100% dense one (in three dimensions). The molecules are remarkably adept at avoiding being trapped. This mimics the effect of so-called leveler molecules which are used in electrochemical deposition.