Münster 1999 – wissenschaftliches Programm

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O: Oberflächenphysik

O 3: Adsorption an Oberfl
ächen (I)

O 3.7: Vortrag

Montag, 22. März 1999, 12:45–13:00, S10

Effect of the cluster size in modelling the H₂ desorption and dissociative adsorption on Si(001) — •E. Penev, P. Kratzer, and M. Scheffler — Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin-Dahlem

Three different clusters, Si₉H₁₂, Si₁₅H₁₆, and Si₂₁H₂₀, are used in density-functional theory calculations in conjunction with ab initio pseudopotentials to study how the energetics of H₂ dissociative adsorption on an d associative desorption from Si(001) depends on the cluster size. The results are compared to five-layer slab calculations using the same pseudopotentials and a high quality plane-wave basis set. Several exchange-correlation functionals are employed. Our analysis reveals that the smaller clusters generally overestimate the activation barriers and reaction energies. The Si₂₁H₂₀ cluster, however, is found to predict reaction energetics, with E_a^des=56 ± 3 kcal/mol (2.4± 0.1 eV), reasonably close to that obtained from the slab calculations. Thus, convergence with increasing cluster size is found to be slow. Differences in the calculated activation energies are discussed in relation to the efficiency of clusters to describe the properties of the clean Si(001)-2×1 surface.