Starting configurations were generated using the Amorphous Cell module of Materials Studio, using PCFF parameters. will place most emphasis on the TZVP lowest-energy configurations, other low-energy configurations will also be considered in those cases where they exhibit pronounced differences from the lowest-energy ones. Generally, the TZVP adsorption energies are between 7% and 13% less negative than the corresponding DZVP values. Larger differences on the order of 17% to 35% were found in a previous rev-vdW-DF2 study considering the adsorption of larger organics having molar masses between 150 and 300 g mol -1 (compared to 130.08 g mol -1 for 5-FU). Altogether, the present work corroborates the previous conclusion that (at least) triple-zeta basis sets are necessary to compute reasonably accurate adsorption energies for sizeable organic molecules in zeolites, which is why the following paragraph will focus on the TZVP results. Looking at the numerical values, an adsorption energy of -73 kJ mol -1 is predicted for purely siliceous FAU. The presence of a single framework proton in H-FAU_1H results in a neardoubling of the interaction strength, with a Δ𝐸 , value of -144 kJ mol -1 . Inclusion of a second proton in the 12MR results in a further increase by about 25%/31% for the "1_3" and "1_4" proton arrangements of H-FAU_2H. If a third proton is present in the same 12MR, however, the adsorption energy is somewhat less negative than for H-FAU_2H, an evolution that can be understood when looking at the local environment of the adsorbed 5-FU molecule (discussed in the following section). For the more Al-rich models containing 16 and 32 protons, ). Typical error bars associated with the AIMD results are on the order of ±10 kJ mol -1 , with the larger error of about ±20 kJ mol -1 for H-FAU_2H_1_4 being an exception. For 5-FU@SiO2-FAU, where two configurations are very close in energy (Config1 and Config2, see Figure ), a total of four AIMD simulations were run, two starting from each configuration. The resulting internal energy of adsorption is about 9% less negative than the Δ𝐸 , value computed with DZVP basis sets. Relative differences obtained for the protonic FAU models show significant scatter, falling between 2% and 13%. Given the error bars of the AIMD-derived Δ𝑈 values, it is clear that these numbers should not be overinterpreted. Nevertheless, it is worth noting that the reduction in interaction strength caused by the inclusion of thermal motion in the simulations is considerably smaller than observed in previous, methodologically analogous investigations of carbamazepine and triclosan adsorption, where differences were on the order of 20% to 30% for all-silica FAU, and amounted to 16% for triclosan in H-FAU_1H. 2) Lowest-energy configurations and hydrogen bonds