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We review the young field of ab initio molecular dynamics applied to molecule-surface reactions. The techniques of ab initio molecular dynamics include methods that use an analytic potential energy function fit to ab initio data and those that are fully ab initio. In this review, we focus on the insights provided by ab initio–based molecular dynamics that are currently unavailable from experimental studies and discuss current techniques and limitations. As an example of how different aspects of a problem can be tackled with state-of-the-art theoretical tools, we consider the well-studied case of H2 desorption and adsorption from the Si(100)-2 × 1 surface.
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Figure 1. Top view of a Si(100) surface that has been exposed to fluorine gas in an ab
initio--derived MD simulation. The grayish white spheres are F atoms, the top
layer of Si is depicted as pink spheres, while the rest (blue spheres) are subsurface
Si. Note the presence of SiF, SiF2, and SiF3 groups on the surface, even at
the low coverage of 1.1 monolayers, and the initial onset of disorder, as illustrated
by the disruption of the (pink) Si dimer rows. [Adapted from Reference 31a (Weakliem
PC, Wu CJ, Carter EA. 1992. Phys. Rev. Lett. 69:200--3).] Figure 2. Snapshots from a fully ab initio MD simulation of H2 desorbing from Si(100),
starting from the transition state for desorption via a dihydride desorption
precursor. The H atoms are the small magenta spheres, the light blue spheres
are silicon atoms, and the dark blue spheres are embedding atoms. Note that
while the structure of the transition state (t = 0) would suggest a very
broad angular distribution, the corrugated nature of the surface allows the
H2 to scatter off of a neighboring dimer and become refocused more toward the
surface normal. [From Reference 91 (da Silva AJr., Radeke MR, Carter EA. 1997.
Surf. Sci. Lett. 381:628--35).]