A generalised vibronic-coupling Hamiltonian model for benzopyran

Area of Science:

• Computational Chemistry
• Theoretical Chemistry
• Molecular Dynamics

Background:

• Existing vibronic coupling models have limitations in describing complex molecular systems.
• Accurate modeling of intersecting potential energy surfaces is essential for understanding nonadiabatic processes.
• Large-amplitude motions and non-Born-Oppenheimer effects present significant challenges in molecular dynamics.

Purpose of the Study:

• To present a novel general model for intersecting multidimensional potential energy surfaces.
• To extend existing vibronic coupling models to handle more complex scenarios.
• To apply the new model to the nonadiabatic photodynamics of benzopyran.

Main Methods:

• Development of a new theoretical framework extending vibronic coupling models.
• Systematic use of curvilinear coordinates.
• Inclusion of a larger number of diabatic states than adiabatic states.
• Application to fitting potential energy surfaces using complete active space self-consistent field (CASSCF) calculations.
• Inclusion of up to 12 active degrees of freedom.

Main Results:

• The developed model successfully describes intersecting potential energy surfaces involving large-amplitude motions.
• Preliminary fittings for benzopyran's nonadiabatic photodynamics show promising results.
• The study emphasizes the physical interpretation of diabatic states and the influence of various degrees of freedom.

Conclusions:

• The new general model provides a powerful extension to existing vibronic coupling theories.
• The approach offers improved capabilities for simulating complex nonadiabatic molecular dynamics.
• The findings are crucial for advancing the understanding of photochemical processes in molecules like benzopyran.