Spin-orbit splittings and spin-orbit coupling matrix elements (SOMEs) were furthermore validated for a benchmark set by Dinkelbach et al. The test set originally comprises 14 organic molecules. For two of the therein included structures, namely furan and thiophen, Dinkelbach et al. explicitly added diffuse basis functions centered at a dummy atom within the five-membered aromatic ring. For convenience and to enable an unbiased validation of all test structures, furan and thiophen were therefore excluded in our benchmark studies. The remaining 12 test molecules are visualized in Fig. , featuring C, O, N, S, and H atoms.