Activation Energies & Volumes

Understanding the Driving Forces for Chemical Dynamics

How can we calculate energetic and entropic barriers?

We are developing novel approaches to calculate activation energies (i.e., roughly the energy barriers) for chemical reactions or transport rates from simulations at a single temperature.  These methods are more accurate than the traditional Arrhenius approach taught in general chemistry classes and present a number of other advantages.  For example, they provide otherwise unavailable mechanistic information in the form of the activation energy contributions from the different motions and interactions of the system. They can also be used to predict the effect of pressure, i.e., determine activation volumes. We have particularly used these approaches to provide new insight into the dynamics of water and aqueous solutions, including accurate calculations of activation energies for water diffusion, reorientation, and hydrogen-bond exchange kinetics along with key mechanistic details. This framework, which we call fluctuation theory for dynamics, is a step toward a comprehensive theory for the driving forces for chemical dynamics.