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 Si(001)-(2 x 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