Dissociative Adsorption of H₂ on the H/Si(100) Surface the Effect of Intradimer π-Bonding Disruption

We have studied dissociative H₂ adsorption on the H/Si(100) surface by means of pseudopotential density functional theory calculations. This work is directly motivated by the observations of Biederman et al. [Phys. Rev. Lett., 83, 1810 (1999)]: "H₂ adsorption is significantly promoted in an interdimer configuration of two adjacent singly occupied dimers." We find that there is no adsorption barrier (in the local site where two quasi-free dangling bonds are available; the adsorption energy is estimated to be 2.6 eV per H₂ within the local density approximation. We present maximally localized Wannier functions that clearly illustrate the behavior of dangling orbitals upon the approach of H₂. The results suggest that intradimer π-bonding disruption is crucial for the significant promotion of H₂ adsorption on Si(100).