Thoroughly exploring the configurational space of atmospheric molecular clusters using, for instance, metadynamics simulations or genetic algorithms at a high level of theory is extremely computationally demanding. Hence, usually, a funneling approach is applied, where the configurational space is initially explored at a low level of theory such as force-field or semiempirical methods, and only a subset of low energy structures is selected, reoptimized, and reexamined at a higher level of theory. This process is repeated with an increasing level of theory until only a few structures remain for evaluation at the desired high level.