Conical Intersections: The Seam Space Between the Sciences

Abstract

When molecules absorb light and become excited, the energy ultimately has to go somewhere; the energy can be lost by radiation, transferred to another molecule, or lost as heat. To predict how molecules interact with light and other matter, theoretical chemists use calculations based on the Born-Oppenheimer Approximation to numerically estimate energies and other properties of interest. Most processes can be explained within the bounds of the approximation; however, the spontaneous nonadiabatic loss of energy as heat cannot. These non- adiabatic processes are driven by conical intersections and play an important role in many known phenomena. Computationally, conical intersections rise out of the breakdown of the Born- Oppenheimer Approximation and the coupling of electronic and nuclear wavefunctions. Physically, conical intersections represent the seam space of degenerate electronic states on the potential energy surface of a molecule. Metaphorically, conical intersections represent the seam space of the research frontiers in biology, chemistry, physics, mathematics, and computer science. The present work is a review of the work in, and application of, each respective field related to conical intersections and a benchmarking study of the most viable current methods used to calculate conical intersections.