Diabatization for Time-Dependent Density Functional Theory: Exciton Transfers and Related Conical Intersections

Area of Science:

• Theoretical Chemistry
• Quantum Chemistry
• Spectroscopy

Background:

• Intermolecular exciton transfer is crucial for energy transport in molecular systems.
• Conical intersections play a significant role in ultrafast dynamics and reaction pathways.
• Accurate theoretical descriptions are needed to understand these phenomena.

Purpose of the Study:

• To develop and apply a diabatization scheme for analyzing intermolecular exciton transfers.
• To investigate the role of conical intersections in these processes.
• To elucidate the contributions of Coulomb (Förster) and electron exchange (Dexter) couplings.

Main Methods:

• Diabatization of adiabatic states obtained from time-dependent density functional theory (TD-DFT).
• Calculation of singlet and triplet exciton couplings, including Förster and Dexter contributions.
• Analysis of charge transfer integrals and diabatic potentials for stacked molecules.

Main Results:

• The diabatization scheme successfully emulates well-defined reference states.
• Singlet exciton coupling incorporates both Coulomb and Dexter contributions.
• Triplet exciton transfers are analyzed for direct and superexchange pathways.
• Specific molecular aggregate topologies inducing conical intersections are identified.
• Selective exciton transfer to dark states is observed due to canceled coupling to bright states.

Conclusions:

• The developed diabatization scheme provides a robust framework for studying exciton dynamics.
• Understanding conical intersections and exciton coupling is key to controlling energy transfer in molecular aggregates.
• The method accounts for Berry phase effects in the diabatic representation.