In order to get a better understanding of the pre-nucleation phase of ZIFs growth we aimed to investigate how clusters increase their stabilities as they grow. Experimentally, the most stable system that it is possible to create with Zn 2+ cations is the infinite, periodic crystal structure of ZIF-zni, but the ωB97X/6-311++G(d,p) calculations we have carried out so far (based on cluster models) cannot be employed to study periodic systems, so we cannot see how the energies of the clusters approach the value of the ZIF-zni crystal structure. To overcome this problem, we carried out two types of periodic calculations: the (very time-consuming) nonlocal SCAN+rVV10 exchange-correlation functional (as implemented in VASP), and the (less costly) GFN2-xTB/ALPB method. Both of these calculations show (see Figure ) that, in agreement with experiments, the most stable crystal structure is that of ZIF-zni, with a formation energy of -6.18 eV (calculated with the GFN2-xTB/ALPB method). This correct prediction of crystal structure stabilities provides further support for the validity of our calculations in clusters presented above.