For the def2-nZVPP family of basis sets, α CBS(2,3) = 10.39 and β CBS(2,3) = 2.40, and α CBS(3,4) = 7.88 and β CBS(3,4) = 2.97. A range of density functionals were used for an exemplary benchmark study to com- pare the different reference levels of theory, and the methods used are listed in table . Each functional was combined with the DFT-D3 and/or DFT-D4 dispersion correction where appropriate. MN15-L calculations were done using the ORCA implementation of the LibXC density functional library. The non-local VV10 82 kernel in B97M-V, ωB97M-V and ωB97X-V was used in its post-SCF implementation, which speeds up the calculation with no impact on the results. 55 ωB97X-2 was used in its "TQZ" parameterisation.