For the computation of orbital energies of NDs with different amounts of sp 2 -hybridized surface coverage, structures were optimized by tight-binding density functional theory (DFT) using the xtb software and default optimization conditions. This yields reasonable structures as discussed in the ESI. On these structures, we performed single point calculations within ORCA 5.0, using the PBE0 hybrid functional , Ahlrich's def2-SVP basis set, Grimme's third order dispersion correction (D3) with Becke-Jones damping, and ORCA's DEFGRID1 option for fast integral calculations. The base structures used for the calculations of orbital energies and absorption spectra were obtained from the CSIRO twinned nanodiamond data set. Most computations were carried out on the high performance computing cluster CURTA by Zentral Einrichtung Datenverarbeitung (ZEDAT) of Freie Universität Berlin.