Simulations of the nucleation of AgBr from solution

We use molecular dynamics to study the nucleation of AgBr in water. After first testing our Born-Mayer-Huggins potentials for Ag+ and Br- by looking at bulk AgBr and at AgBr clusters in vacuo, we consider small numbers of Ag+ and Br- ions immersed in water. The system shows the expected qualitative features of nucleation form solution, including a critical cluster size that decreases with increasing concentration. However, we find that for cluster sizes at least as large as Ag18Br18, the most stable cluster is disordered. This is in stark contrast to clusters in vacuo where clusters as small as Ag4Br4 from ordered fragments of the lattice. These results lend some support to the conjecture that nucleation of crystals from solution is a two-stage process with the first stage consisting of the formation of disordered clusters of solute and the second stage involving the nucleation of a crystal from this solute "melt." (C) 2000 American Institute of Physics. [S0021-9606(00)50839-3].