To allow for a more direct comparison with the conditions in previous DFT simulations, all the water molecules are removed and then the total potential energy (U ) is optimized. The optimization is performed by the steepest descent method followed by the application of the conjugate gradient algorithm. The combination of these two techniques allows for the identification of the nearest minimum of U for each starting structure. A threshold of 10 • 10 -5 k B T / Å is used for convergence of the forces.