Nonorthogonal Multireference Wave Function Description of Triplet-Triplet Energy Transfer Couplings

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Theoretical Chemistry

Background:

• Energy transfer (EnT) processes are crucial in chemistry and biology.
• Accurate calculation of diabatic coupling elements is essential for understanding EnT kinetics.
• Existing methods face challenges, particularly with orbital relaxation effects.

Purpose of the Study:

• To investigate the utility of self-consistent field (SCF) quasi-diabats for calculating triplet EnT diabatic coupling elements.
• To introduce a conceptual model for simultaneous evaluation of direct and charge-transfer EnT mechanisms.
• To assess the performance of SCF quasi-diabats using model systems.

Main Methods:

• Utilized self-consistent field (SCF) quasi-diabats.
• Developed a conceptual model for simultaneous evaluation of direct and charge-transfer mechanisms.
• Applied the method to the ethylene dimer and ethylene-methaniminium cation systems.

Main Results:

• SCF quasi-diabats implicitly include orbital relaxation, beneficial for EnT studies.
• The model allows simultaneous assessment of direct and charge-transfer mechanisms.
• Charge-transfer mechanisms, though higher in energy, showed significantly larger coupling elements, influencing kinetics.

Conclusions:

• SCF quasi-diabats provide an advantageous approach for calculating triplet EnT coupling elements.
• The method addresses practical limitations of established techniques.
• This approach enhances the understanding of competing energy transfer pathways.