New Algorithms for Optimizing and Linking Conical Intersection Points.

Area of Science:

• Computational Chemistry
• Theoretical Chemistry
• Quantum Chemistry

Background:

• Understanding conical intersections is crucial for studying non-adiabatic processes in molecular systems.
• Accurate characterization of seam geometries and energies is essential for predicting reaction dynamics.

Purpose of the Study:

• To develop and present two new algorithms for the investigation of conical intersections between electronic potential energy surfaces.
• To enable optimization of conical intersection geometries, including minima and saddle points, with arbitrary constraints.
• To provide a method for explicitly computing the minimum energy coordinate within the intersection space.

Main Methods:

• Algorithm 1: Optimization of conical intersection geometries (minima and saddle points) with geometrical constraints.
• Algorithm 2: Explicit computation of the intersection-space minimum energy coordinate.
• Demonstration on model systems: benzene, z-penta-3,5-dieniminium, and 1,3-butadiene.

Main Results:

• The first algorithm successfully optimizes conical intersection geometries under various constraints.
• The second algorithm unambiguously defines intersection seams and their associated energies.
• A portion of the S0/S1 1,3-butadiene crossing seam was mapped, revealing a new saddle point connecting lower-lying geometries.

Conclusions:

• The presented algorithms offer robust tools for studying conical intersections and seam properties.
• These methods advance the accurate characterization of non-adiabatic reaction pathways.
• The findings provide deeper insights into the topology and energetics of crossing seams in molecular systems.