Dresden 2011 – wissenschaftliches Programm

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DY: Fachverband Dynamik und Statistische Physik

DY 30: Reaction-Diffusion Systems

DY 30.9: Vortrag

Donnerstag, 17. März 2011, 12:15–12:30, ZEU 118

Activation parameters of model redox reactions and their variation from classical molecular simulation — •Christof Drechsel-Grau and Michiel Sprik — University of Cambridge, Department of Chemistry, Cambridge, CB2 1EW, United Kingdom

Transition states are dynamical bottlenecks of chemical reactions, and an understanding of their energetic properties and location can provide insight into the reactions' mechanism. In particular, the variation of the activation free energy with temperature yields the activation entropy and the activation energy, whereas the variation of the activation free energy with reaction free energy defines the charge-transfer symmetry factor, which indicates the location of the transition state relative to the stable states. The calculation of activation parameters is not only computationally demanding, but traditionally also relies on knowledge of the reaction coordinate, which is usually unavailable. Thus, we employ transition path sampling, which does not require knowledge of the reaction coordinate, to compute activation energies and their variation with reaction free energy for a model system. Exploiting knowledge of the reaction coordinate for the model system, we also calculate the activation free energies and the charge-transfer symmetry factor from umbrella integration and from free energy perturbation simulations. We find that the activation energies are smaller than the activation free energies. In addition, the variation of the latter with reaction free energy is larger than that of the former.