Acetylene adsorption on silicon (100)-(4 × 2) revisited

The aim of this work is to revisit the problem of acetylene adsorption on silicon (100). Extending previous theoretical work and including van der Waals forces explicitly in the simulations we remove existing ambiguities about the adsorption sites. The simulated adsorption energies and scanning tunneling microscopy contours are in good agreement with experimental data, they support the interpretation of a two-dimer feature at the surface as resulting from the adsorption of two individual molecules. It is also found that the simulated apparent heights agree with experimental values, if the actual bandgap of silicon is taken into account.