Reaction coordinate in chemistry: fool's gold, or an actionable concept?
Pratyush Tiwary, University of Maryland, College Park


The reaction coordinate (RC) is an ubiquitous concept across chemistry, found in the introductory chapters of arguably all physical chemistry textbooks. The usefulness of many widely used theories and methods - transition state theory and umbrella sampling to name a couple - is contingent upon knowing the RC. In principle the RC is a low-dimensional descriptor that best captures the movement of a given high-dimensional system from one metastable state to another. But most real world systems do not have just two states, and are characterized by multiple spatiotemporal scales and numerous intertwined degrees of freedom. Identifying what the RC is for these systems becomes a very hard problem. Furthermore, the RC can also dynamically alter depending on the nature and extent of coupling with the solvent or the environment. In this talk, I will first re-examine the notion of what an RC actually is. I will then describe some new methods for finding the RC in complex molecular systems characterized by rare events. Finally, I will show some applications of these methods with a special focus on the structural dynamics of drug unbinding using fully atomistic simulations of biotin-streptavidin and protein kinases relevant to cancer.