We were pleased to welcome Prof. Bettina Keller from Freie Universität Berlin to the Atomistic Modeling Seminar as this term’s second speaker. Bettina Keller has been Professor for Theoretical Chemistry at Freie Universität Berlin since 2019. Her research focuses on molecular dynamics simulations and models of reaction networks.

In her talk, “Thermal isomerization of retinal: the interplay between reaction coordinates and entropy”, Prof. Keller discussed how reaction dynamics have traditionally been described using Eyring Transition State Theory (TST), and how recent advances in potential energy surfaces, particularly those based on neural networks, enable simulations beyond these traditional limitations.

She addressed the role of reaction coordinates in enhanced sampling and in interpreting the underlying free-energy landscape, and discussed the relation between reaction coordinates, committors, and entropy. Using the thermal cis–trans isomerization of retinal as a case study, she examined how entropic effects shape the reaction pathway.

The seminar provided valuable insights into reaction dynamics, the role of reaction coordinates, and the effects of entropy.

Date: Tuesday, April 14, 2026, 10:30 am

Location: MIBE Lecture Hall

Abstract:

Reaction dynamics have traditionally been described using Eyring Transition State Theory (TST), a framework that, while successful for small gas-phase molecules, is constrained by its rigid assumptions. Recent advances in potential energy surfaces, particularly those based on neural networks, now enable simulations that extend beyond these traditional limitations, capturing anharmonic reactants and transition states, as well as systems with multiple subminima in the reactant or transition-state regions.

In complex systems, identifying an appropriate reaction coordinate is essential not only for enhanced sampling but also for interpreting the underlying free-energy landscape. The free energy along a coordinate reflects a balance between energetic contributions and the entropy associated with configurations orthogonal to it. The committor function provides a rigorous, kinetic definition of reaction progress, and its relation to a chosen coordinate offers a way to disentangle enthalpic and entropic contributions to the reaction barrier.

The talk will explore the interplay between reaction coordinates, committors, and entropy, and how these concepts help interpret simulation data and assess rate predictions beyond TST. As a case study, the thermal cis–trans isomerization of retinal will be examined, highlighting how entropic effects shape the reaction pathway.