Chemistry beyond Born–Oppenheimer
A New Spin on the Waltz of Electrons and Nuclei
The Born–Oppenheimer approximation provides much of the conceptual language of chemistry. By separating electronic and nuclear motion, it allows us to describe molecules in terms of potential-energy surfaces, molecular structures, reaction pathways, barriers, and transition states.
Time: Thu 2026-10-01 10.00
Location: K-building. Erdtman room
Language: English
Participating: Nanna Holmgaard List, Docent in Theoretical Biochemistry
Yet this picture becomes insufficient when electronic and nuclear motion are strongly coupled, as commonly occurs following the absorption of light. In this lecture, I will discuss conical intersections – regions where potential-energy surfaces meet – and how they provide pathways for molecules to rapidly switch between electronic states.
Such processes are central to light-driven chemistry, from enabling vision and protecting us from harmful UV radiation to powering molecular machines and using light to make chemistry happen. I will discuss how state-of-the-art nonadiabatic dynamics can be used to understand, and increasingly predict, such processes.
Finally, I will look beyond the usual treatment of electronic motion by considering electron spin. Spin is traditionally treated as a property of electronic states that influences their energies and which reaction pathways are accessible, rather than as a dynamical degree of freedom coupled to molecular motion. Yet emerging observations of spin-dependent chemistry challenge this picture.
I will discuss our efforts to develop a description in which electronic, nuclear, and spin degrees of freedom can exchange angular momentum dynamically, and how this may open new ways of understanding and ultimately controlling chemical reactivity.