xTB was originally parameterized from the spincomponent-scaled coupled cluster (SCS-CC2) method and TD-DFT, so one of these would be a natural choice as the reference computational technique. Coupled-cluster (CC) methods are typically the most accurate, predicting excitation energies within 0.1 eV of experiment. However, because of the computational expense of CC, it is difficult to generate a large amount of data using these methods. Instead, TD-DFT is generally the workhorse for excited state calculation, despite its relatively high errors, with an MAE of 0.2 to 0.4 eV (depending on the functional) compared to experiment or the theoretical best estimate. A general-purpose exchange-correlation functional is B3LYP , which has been shown to have an MAE around 0.25 eV, while LDA, GGA, and other hybrid functionals have higher error. While B3LYP performs well for local-ized densities, range-separated hybrid functionals such as CAM-B3LYP are increasingly used for delocalized densities such as those in excitations as they include a long-range correction. However, these range-separated hybrid functionals are more computationally expensive than B3LYP. Due to its accuracy and efficiency, B3LYP is the most commonly used functional in computational molecular chemistry. In this work, we choose TD-DFT based on B3LYP as the reference method, for several reasons. First, we require large chemical diversity in our training set, and most of the existing molecular excited state databases use TD-DFT. The largest databases, namely PubChemQC and QM-symex, use B3LYP. Second, B3LYP was used in previous works using linearly calibrated xTB-sTDA and is used extensively in machine learning and high-throughput screening studies. Third, while B3LYP is less accurate than range-separated hybrid functionals, it is not significantly worse. Since xTB-sTDA is semi-empirical, it is often used as a first-pass screening and naturally has inconsistencies and false positive/negative errors. Calibrating to B3LYP accuracy should lower the rate of these errors. For these reasons, the reference method was chosen to be TD-DFT with B3LYP.