New Optimization Methods for Electronic Excited States Todd J. Martinez (Chemistry)

1. New Optimization Methods for Electronic Excited States Todd J. Martinez (Chemistry) ResearchObjectives: Understanding the chemical reactivity of excited electronic states requires knowledge of molecular geometries where one or more electronic states have the same energy. These geometries are known as conical intersections and play a key role in solar cells and human vision. Approach: We have developed a new method for determining these intersection geometries which is broadly applicable to all electronic structure methods that can treat excited states. Significant Results: We have used the new optimization method to optimize intersection geometries for a number of molecules which are paradigmatic in photochemistry. The flexibility and efficiency of the new method allowed us to carry out these optimizations with the most accurate electronic structure methods available, providing benchmark results for more approximate methods. Comparison of potential energy surfaces near a conical intersection at two levels of theory. Intersection optimization at the accurate MS-CASPT2 level of theory was impossible before the introduction of our new method. Broader Impact: The new optimization method has been implemented to allow interfacing to any electronic structure code and is freely available to researchers through the MCC Software Archive.