Transition orbital projection approach for excited state tracking

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Theoretical Chemistry

Background:

• Comparing electronic excited states (ESs) is essential for potential energy surface (PES) studies and excited-state fragmentation.
• Current methods struggle with complex and degenerate systems, posing a significant challenge.

Purpose of the Study:

• To introduce a robust method for quantitatively comparing features between different electronic excited states.
• To address limitations in existing approaches for complex and degenerate systems.

Main Methods:

• Developed the transition orbital projection (TOP) method to calculate ES similarity.
• Utilized configuration vectors of transition densities, addressing phase, bijectivity, permutation, and sign issues.
• Implemented TOP for state-tracking-based excited-state optimization.

Main Results:

• TOP method demonstrated high robustness in optimizing excited states of highly symmetric systems.
• Successfully overcame limitations of traditional state-tracking approaches.
• The method accurately compares complex and degenerate electronic excited states.

Conclusions:

• The TOP method provides a reliable way to compare electronic excited states.
• Expected to advance PES studies in photochemistry, excited-state molecular dynamics, and fragmentation approaches.
• Enhances the study of local excitations in large molecular systems.