doi:10.1016/S0013-4686(03)00508-5 
Copyright © 2003 Elsevier Ltd. All rights reserved.
Ab initio and classical molecular dynamics studies of electrode reactions
Christoph Hartnig1, Peter Vassilev and Marc T. M. Koper
, 
, 2
Schuit Institute of Catalysis, Laboratory of Inorganic Chemistry and Catalysis, Eindhoven University of Technology, 5600 MB, Eindhoven, Netherlands
Received 14 November 2002;
revised 10 February 2003;
accepted 11 February 2003. ;
Available online 2 September 2003.
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Abstract
A brief overview is given of some recent applications from our group of classical molecular dynamics (MD) and ab initio molecular dynamics (AIMD) simulations to the study of electrode reactions. Classical MD simulations are used to study solvent reorganization in outer-sphere electron transfer (ET) reactions, the first step in the oxygen reduction reaction, and ion transfer. AIMD simulations are used to study the structure of a water–vapor interface, and the mobility of solvated OH species on a Rh(111) surface by a proton transfer reaction between surface-bonded OH and a neighboring water molecule.
Author Keywords: Molecular dynamics; Electrode reactions; Density functional theory; Electron transfer
Fig. 1. Pictorial sketch of solvent reorganization and free energy curves for an outer-sphere ET reaction Oxn++e−↔Red(n−1)+ in the Marcus theory.
Fig. 2. Free energy surfaces for ET. Solid lines give MD-generated free energy curves for Cl
2−, Cl
−, Cl, and Cl
+; dashed lines give parabolic fits to the minima.
Fig. 3. The Cl---O pair radial distribution function as a function of the generalized solvent coordinate. Numbers indicate the corresponding values of the reaction coordinate (in kJ mol
−1).
Fig. 4. The Cl---H pair radial distribution function as a function of the generalized solvent coordinate. Numbers indicate the corresponding values of the reaction coordinate (in kJ mol
−1).
Fig. 5. Free energy surfaces for the solvent reorganization in
reaction 2 as generated from MD simulations. Dashed lines give parabolic fits to the minima.
Fig. 6. Two-dimensional free energy surface for the Cl
−/Cl adsorption on a flat featureless wall as generated from MD simulations.
z is the distance of the atom/ion center from the wall. The channel near −550 kJ mol
−1 is the Cl
−; the channel at approximately −50 kJ mol
−1 is the Cl atom.
Fig. 7. (a) Density distribution of the water–vapor interface along the z axis. The solid and dotted line correspond to the oxygen and hydrogen distributions from a 4 ps AIMD simulation. The dashed line (shifted by 1 unit to clearly distinguish between AIMD and classical MD results) corresponds to the oxygen distribution from a 250 ps classical MD simulation with the same number of 32 molecules in the same simulation cell. The preferred orientation of the water molecules concluded from the AIMD is shown on the right. L1, L2, and L3 are the notations for the three water layers in the slab. (b) Normalized angular distributions of the water dipole. Solid, dotted and dashed lines correspond to the L1, L2, and L3 layers, respectively.
Fig. 8. Subsequent configurations in the chain of proton exchange reactions between neighboring OH and H
2O molecules leading to an effective “shift” in the position of the surface hydroxyl. The Rh(111) surface is in the
x−
y plane.
Fig. 9. Top view of the local environment of the surface hydroxyl species. The metal surface is in the plane of view. O* is the oxygen of the hydroxyl, O
c are the oxygens of the complexing water molecules, O′ is the oxygen of the nearest non-complexing water.
Table 1. Solvent reorganization energies estimated from classical MD simulations for 3+, 2+, 1+, 0, 1−, 2−, 3− species with a hard-core representing chloride
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