In this study three length scales are treated for studying ZIF nucleation: smaller clusters are studied using non-periodic Density Functional Theory (DFT); for extended clusters we turn into the less expensive semiempirical tight-binding (TB) calculations; while periodic DFT and TB approaches are used to model infinite crystalline ZIFs. The calculations to study the stability of ZIF clusters with up to six Zn 2+ cations and a reduced number of explicit H 2 O or CH 3 OH solvent molecules, or NO - 3 counterions were performed with the Gaussian 09 (Revision A.02 code). The computations used the long-range corrected hybrid density functional ωB97X, to account for van der Waals interactions and the large 6-311++G(d,p) triple-ζ basis set with polarization and diffuse functions, in order to reduce basis set superposition errors. Since energy minimization of zeolitic materials containing water or other strongly interacting solvent molecules requires very long computational times, 41 implicit solvation has also been considered (more details below) by means of the Self-Consistent Reaction Field, using the Polarizable Continuum Model (PCM), which takes into account the solvent implicitly, -i.e. it does not include the explicit presence of solvent molecules, but it does include the electrostatic effects that they would have over the reactants. We have included the PCM parameters to mimic the effect of ethanol using the default parameters in Gaussian (ϵ = 24.852, and UFF atomic Van der Waals radius).