In Part 1, adsorption energies are computed for a variety of organic species in two all-silica zeolites (MOR and FAU), with the choice of adsorbents and adsorbates following previous experimental and computational work. In addition to evaluating the differences in absolute adsorption energies, it is also assessed whether different functionals deliver any appreciable differences in the relative trends. It should be emphasised that this work does not attempt to obtain DFT-computed adsorption energies that could be directly compared to any observable quantity. Instead, the key aim is to identify trends within the set of dc-XC functionals, and to benchmark them against higher-level calculations, at least for a selection of models. On this basis, some recommendations regarding their probable suitability can be made, allowing to use them with confidence in future, more practically oriented studies dealing with the adsorption of emerging organic contaminants or similarly complex organic molecules in zeolites.