Excitonic couplings between molecular crystal pairs by a multistate approximation.

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Materials Science

Background:

• Accurate computation of excitonic couplings is crucial for understanding energy transfer in molecular systems.
• Existing diabatization schemes often struggle with systems involving more than two electronic states.
• Organic crystals present complex excitonic behavior due to multiple closely spaced energy states.

Purpose of the Study:

• To develop a novel diabatization scheme for computing excitonic couplings between an arbitrary number of states in molecular pairs.
• To provide a versatile method applicable to various electronic structure calculations and state types.
• To validate the scheme's efficacy in systems relevant to organic electronics, such as organic crystals.

Main Methods:

• An algebraic procedure is employed to identify diabatic states closely matching reference states.
• The scheme inherently includes short-range contributions: exchange, overlap, and charge-transfer terms.
• The method is tested on a tetracene crystal dimer, analyzing the influence of external electric fields and intermolecular distances.

Main Results:

• The diabatization scheme successfully computes excitonic couplings for multiple states, outperforming existing methods in complexity.
• Validation on the tetracene dimer demonstrates accurate prediction of couplings between Frenkel excitons (FE) and charge-transfer (CT) states.
• The study shows the scheme's capability to incorporate environmental effects, such as polarization, and analyze field-dependent behavior.

Conclusions:

• The presented diabatization scheme offers a robust and flexible approach for calculating excitonic couplings in complex molecular systems.
• Its applicability to organic crystals and ability to handle multiple states make it valuable for designing advanced organic electronic materials.
• The method provides a pathway to accurately model exciton-exciton and exciton-charge transfer interactions, crucial for device performance.