Adaptable Range-Separated Hybrids for the Description of Excited States: Tuning the Range Separation Parameter on Effective Charge Transfer Distance

In this contribution, we describe a novel approach, rooted in the time-dependent density functional theory, enabling to adapt range-separated hybrids (RSHs) to correctly describe excited states (ESs) of inter- and intramolecular charge transfer (CT) character. Contrary to previous works enforcing the fulfillment of Koopmans’ theorem, here, the range-split parameter of RSHs is tuned so as to constrain it in the range of distances corresponding to the hole–electron separation occurring in target CT states for the molecule of interest. The procedure proposed, while not requiring a fit but only an estimate of the CT distances for all ESs of interest, is not based on empirical adjustment and enables finding a system-dependent range separation parameter optimal for the treatment of CT states while not deteriorating its performances with respect to low Hartree–Fock exchange global hybrids for the description of ESs of a more local character. The results obtained for a series of CT compounds show the very good accuracy of this adaptative tuning procedure of RSHs and its potential to explore the ES behavior of molecular systems.