DFT Functional Uncertainty. Unfortunately, the agreement between measured and computed "gap" does not yet take the most prominent systematic error of DFT into account, which arises from the employed approximate DFT exchange and correlation functional. At the present level of semi-local functionals together with an additional dispersion correction, this specifically translates to the choice of the prior and the choice of the latter, as well as of the combination of both. As stated initially, little information is hitherto available concerning the suitability of prevalent functionals and dispersion corrections for liquid metal catalysts. To this end, we evaluate the sensitivity of the determined "gap" of Gr on liquid Cu and other liquid metal properties by training MTP potentials with DFT data computed with different functionals and dispersion corrections. This way, the ML surrogate models establish a generally applicable avenue to quality control of DFT by enabling the simulation of experimental observables that would not be feasible at the direct DFT level.