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.