Quantum Chemical Cluster Models for Chemi- and Physisorption of Chlorobenzene on Si(111)-7×7

Abstract

Motivated by recent atomic manipulation experiments, we report quantum chemical calculations for chemi- and physisorption minima of chlorobenzene on the Si(111)-7×7 surface. A density functional theory cluster approach is applied, using the B3LYP hybrid functional alongside Grimme's empirical dispersion corrections (D3). We were able to identify chemisorption sites of binding energies of 1.6 eV and physisorption energies of 0.6 eV, both in encouraging agreement with the trend of experimental data. The cluster approach opens up the possibility of a first-principles based dynamical description of STM manipulation experiments on this system, the interpretation of which involves both the chemi- and physisorbed states. However, we found that special care has to be taken regarding the choice of clusters, basis sets, and the evaluation of the dispersion corrections.

Local resonances in STM manipulation of chlorobenzene on Si(111)-7×7: performance of different cluster models and density functionals

“…Here, we start, as in Refs. [25,34], from a DFT slab structure taken from Ref. [37] with a unit cell consisting of 498 atoms in 12 layers arranged in the so-called dimer-adatom-stacking fault structure [38].…”

“…[25]. Therefore, we demand a deviation of less than 20 % of the binding energy as a quantitative measure and that no difference in the qualitative energetic preference for specific adsorbate orientations should occur.…”

“…[25]. With this methodology, we could successfully model the chemisorption and physisorption for neutral clusters and publish a value for the chemisorption energy, which differed significantly from theoretical and experimental results at that time.…”

“…We characterised physisorbed and chemisorbed chlorobenzene using a cluster approach and density functional theory (DFT) in Ref. [25]. These calculations used a di-σ bonded structure involving adjacent adatoms and rest-atoms on the Si(111)-7×7 surface as reported in Ref.…”

“…[26] based on high resolution electron energy loss spectroscopy data and previous STM experiments [27] (see Ref. [25] and references therein for details about the different adsorption sites in the 7×7 unit cell). The calculated adsorption energies were 1.6 eV (chemisorption) and 0.6 eV (physisorption).…”