  The density functional theory (DFT) approximations that are the most accurate
for the calculation of band gap of bulk materials are hybrid functionals like
HSE06, the MBJ potential, and the GLLB-SC potential. More recently, generalized
gradient approximations (GGA), like HLE16, or meta-GGAs, like (m)TASK, have
proven to be also quite accurate for the band gap. Here, the focus is on 2D
materials and the goal is to provide a broad overview of the performance of DFT
functionals by considering a large test set of 298 2D systems. The present work
is an extension of our recent studies [Rauch et al., Phys. Rev. B 101, 245163
(2020) and Patra et al., J. Phys. Chem. C 125, 11206 (2021)]. Due to the lack
of experimental results for the band gap of 2D systems, $G_{0}W_{0}$ results
were taken as reference. It is shown that the GLLB-SC potential and mTASK
functional provide the band gaps that are the closest to $G_{0}W_{0}$.
Following closely, the local MBJ potential has a pretty good accuracy that is
similar to the accuracy of the more expensive hybrid functional HSE06.
