Embedding Methods: Improvements, Extensions, and Chemisorption of Methane on Ni(100)
Judith B. Rommel (Department of Chemistry, University of Cambridge, UK)

Chemisorption plays an important role in a huge number of industrial processes such as for example the steam-reforming of methane during the Haber–Bosch process. The understanding of gas-surface reactions is key to improve the efficiency of catalysts involved. The chemisorption of methane on a single crystal metal surface, like Ni(100), is a prototypical system to study these processes. Experimental investigations gave clear evidence that transition state theory does not always offer an accurate description of gas-phase surface reactions. Theoretical studies hint that in CH4 dissociative adsorption quantum effects such as tunnelling become important below a surface temperature of 200 K which is far above the predicted classical-quantum crossover temperature. To understand the influence of quantum effects on these reactions we require

1. reliable model potentials to test our theories and

2. a rate theory for non-separable multidimensional systems consistent over the quantum and classical temperature regimes.

Embedded atom methods,1,2 modified and enhanced over the last decades, are popular models to describe structural, mechanical, and thermal properties of metallic systems due to their scaling in performance compared to first-principles calculations. In this presentation I will address the following questions:

• Where do several of these models break down, e.g., D.G. Truhlar’s EAM and M.I. Baskes’ MEAM for CH4 on Ni(100)?

• How can existing models be improved?

• How can we choose a good model?

Ultimately, the improved model in combination with the extended instanton rate theory will increase the understanding of the mechanism of chemisorption in the complete temperature range and will lead to the design of new optimised catalysts.

1 M.S. Daw and M.I. Baskes. Phys. Rev. Lett. 50 (17), 1285 (1983).

2 M.S. Daw and M.I. Baskes. Phys. Rev. B 29 (12), 6443 (1984).