The diffusion of H on the (001) surface was studied by using the tight binding local density approximation to density functional theory. The calculation of the energy of H diffusing on (001) was difficult because, in particular, the bonding at the saddle point was likely to be far from equilibrium. The unit cell which was used for these calculations was 6 dimers long and one dimer wide, with ten layers of Si in the slab. The bottom 5 layers of Si were constrained to lie in bulk-like positions, and the final layer was terminated in H. The only constraint which was applied was that the H should lie in planes of constant y-parameter. The H was allowed to bond to only two Si atoms; the one at which it started, and the one at which it ended. Another atom to which it could have bonded was the second-layer atom to which the 2 dimers were bonded, but this would have led to unphysical behavior. It was concluded that tight binding could describe the diffusion reaction well, if a suitable correction was applied.

Hydrogen Diffusion on Si(001) Studied with the Local Density Approximation and Tight Binding. D.R.Bowler, M.Fearn, C.M.Goringe, A.P.Horsfield, D.G.Pettifor: Journal of Physics - Condensed Matter, 1998, 10[17], 3719-30