Optimizing Conical Intersections without Explicit Use of Non-Adiabatic Couplings.

Area of Science:

• Quantum Chemistry
• Computational Chemistry
• Theoretical Chemistry

Background:

• Minimum energy conical intersections (MECIs) are crucial for understanding non-adiabatic processes in photochemistry.
• Optimizing MECI geometries typically requires knowledge of the derivative coupling (DC), which can be computationally expensive.
• Developing derivative coupling-free methods for MECI optimization is highly desirable.

Purpose of the Study:

• To present two novel, derivative coupling-free methods for optimizing minimum energy conical intersection (MECI) molecular geometries.
• To demonstrate the efficacy of these methods using small molecular systems and specific challenging cases.

Main Methods:

• The proposed methods utilize Lagrange multipliers for MECI optimization.
• One method employs an approximate calculation of the derivative coupling (DC).
• The second method completely avoids the need for DC calculation, relying on the Hessian of the squared energy difference.

Main Results:

• Both presented methods successfully optimize MECI geometries for tested molecular systems.
• The methods show comparable or superior performance to existing techniques.
• The S₁/S₂ MECI of furimamide and the S₀/S₁ MECI of the silver trimer were successfully optimized and characterized.

Conclusions:

• The developed derivative coupling-free methods offer efficient and reliable alternatives for MECI geometry optimization.
• These methods provide valuable tools for studying non-adiabatic dynamics in complex molecular systems.
• The approach based on the Hessian of the squared energy difference is particularly promising for future applications.