Determining Minimum Energy Conical Intersections by Enveloping the Seam: Exploring Ground and Excited State...

Area of Science:

• Computational chemistry
• Theoretical chemistry
• Photochemistry

Background:

• Minimum energy conical intersections (MECIs) are crucial for understanding photochemical reactions.
• Locating MECIs is computationally challenging, often requiring nonadiabatic coupling vectors.
• Coupled cluster (CC) theory can face numerical artifacts at conical intersections.

Purpose of the Study:

• To develop and evaluate an algorithm for locating MECIs that bypasses the need for nonadiabatic coupling vectors.
• To address and overcome convergence issues associated with CC theory at conical intersections.
• To assess the accuracy of CC singles and doubles (CCSD) model for describing MECI geometries.

Main Methods:

• An algorithm that minimizes energy on hypersurfaces enveloping the intersection seam.
• Constraining electronic states to have a small, non-zero energy difference to avoid numerical issues.
• Utilizing coupled cluster singles and doubles (CCSD) model for geometry optimization.

Main Results:

• The algorithm successfully locates MECIs without calculating nonadiabatic coupling vectors.
• Constraining energy differences prevents numerical artifacts and convergence problems in CC theory.
• CCSD model accurately describes the geometries of MECIs with the ground state for various systems.

Conclusions:

• The developed algorithm provides a robust method for finding MECIs.
• Coupled cluster theory, specifically CCSD, can reliably describe the geometries of minimum energy conical intersections.
• This approach suggests potential for using CC theory in nonadiabatic dynamics simulations for ground state relaxation.