Outer layer Inner Layer The integration of the xTB family into the ONIOM framework is demonstrated using the example of UiO-66. In recent work, this Zr-based metal-organic framework (MOF) was modeled as an octahedral cage, consisting of six metal nodes and a total of 484 atoms, as shown in Fig 4 . The cage was optimized by varying the size of the inner region, considering one, three, and six nodes, and using pure as well as intermixed methods (DFT, DFT//GFN, GFN).