  Modelling the inorganic exciton contribution to 2D hybrid organic-inorganic
perovskites is essential to understand their properties and screen for new
materials. Here, we combine hybrid density functional theory calculations
including spin orbit coupling (SOC) with the experimental relationship between
the inorganic band gap and exciton binding energy to predict the inorganic
exciton energy. For this purpose, we determine a universal exchange parameter
for the HSE06 hybrid functional with SOC for lead-based 2D hybrid
organic-inorganic perovskites. We further identify a relationship that connects
PBE calculations to experiment-quality optical gaps and allows us to generalize
the exchange mixing parameter other SOC approximations. Our approach opens the
path to screen for 2D hybrid organic-inorganic perovskites with optimized
spectra, e.g., for new solar cell or light emitting materials.
