  We discuss the system-specific optimization of long-range separated density
functional theory (DFT) for the prediction of electronic properties relevant
for a photocatalytic cycle based on an Ir(III) photosensitizer (IrPS). Special
attention is paid to the charge-transfer properties, which are of key
importance for the photoexcitation dynamics, but and cannot be correctly
described by means of conventional DFT. The optimization of the
range-separation parameter using the $\Delta$SCF method is discussed for IrPS
including its derivatives and complexes with electron donors and acceptors used
in photocatalytic hydrogen production. Particular attention is paid to the
problems arising for a description of medium effects by means of a polarizable
continuum model.
