Metals have a continuous electronic structure without any energy separation between the filled and empty electronic states (bands) while in semiconductors an energy gap separates the occupied (valence) bands from the empty (conduction) bands as shown in Figure . The presence of a band gap in SCEs means that the Fermi-level, and hence the absolute potential on the vacuum scale (Eq.( )), cannot be varied continuously in standard DFT approaches using surface slab models while this is possible experimentally and through the advanced DFT models. Furthermore, it is well-known that capturing the band gap even qualitatively with DFT requires the use of more advanced functionals than needed for metallic systems. Typically, functionals that improve the description of localized electrons or strong electronic correlation, such as +U-corrected, meta-GGA or hybrid functionals, are needed. Besides the functional choice, the number of k-points used for sampling the electronic structure in the reciprocal space needs to be handled with care, because SCEs seem to require substantially higher k-point densities than metals to accurately model the band gap region. However, capturing the band gap is not enough as the edges of the valence and conduction band electronic levels need to be correctly aligned with respect to a reference state, often the vacuum as shown in Figure . This is of crucial importance as the absolute energy level positions directly impact the SCE's electrode potential on the absolute electrode potential scale as can be seen from Eq. (2).