Computational chemistry is used here to rationalize zeolite nucleation and crystallization by means of atomistic molecular mechanic techniques. it is shown that, by isomorphous substitution of Ge by Si, the relative rate of crystallization can be reversed in a series of zeolite structures that compete to nucleate and grow under certain synthesis conditions. This is demonstrated for EU-1, ITQ-13, ITQ-22, and ITQ-24 structures.