Influence of van der Waals forces on the adsorption structure of benzene on silicon studied using density functional theory

Two different adsorption configurations of benzene on the $\mathrm{Si}\left(001\right)\text{−}(2\times 1)$ surface, the tight-bridge and butterfly structures, were studied using density functional theory. Several exchange and correlation functionals were used, including the recently developed van der Waals density functional (vdW-DF), which accounts for the effect of van der Waals forces. In contrast to the Perdew-Burke-Ernzerhof (PBE), revPBE, and other generalized-gradient approximation functionals, the vdW-DF finds that, for most coverages, the adsorption energy of the butterfly structure is greater than that of the tight-bridge structure.

Figure 1

(Color online) BF (top) and TB (bottom) structures of ${\mathrm{C}}_6{\mathrm{H}}_6$ on $\mathrm{Si}\left(001\right)\text{−}(2\times 1)$. Left hand side: viewed along $\left[\overline{1}10\right]$. Right hand side: viewed along [110] dimer rows.