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

Abstract

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.