Application of van der Waals Density Functional to an Extended System: Adsorption of Benzene and Naphthalene on Graphite

It is shown that it is now possible to include van der Waals (vdW) interactions via a nonempirical implementation of density functional (DF) theory to describe the correlation energy in electronic structure calculations on infinite systems of no particular symmetry. The vdW-DF theory [Phys. Rev. Lett. 92, 246401 (2004)] is applied to the adsorption of benzene and naphthalene on an infinite sheet of graphite, as well as the binding between two graphite sheets. A comparison with recent thermal-desorption data [Phys. Rev. B 69, 155406 (2004)] shows great promise for the vdW-DF method.

Figure 1

The lateral configuration of the $AB$ adsorption positions for the molecules benzene and naphthalene on a graphene sheet. Carbon atoms are shown in black, when belonging to the substrate and gray, when belonging to the adsorbate. Hydrogen atoms are shown in white.

Figure 2

Binding-energy curve for two graphene sheets in $AB$ stacking. The calculated general geometry vdW-DF curve (solid line) indicates a binding energy of $45.5\mathrm{meV}/\mathrm{\text{atom}}$ at the equilibrium separation 3.6 Å, which is close to the experimental energy estimates (diamonds with energy error bars; see text). The two vertical dashed lines mark the positions of the potential-energy minimum (3.6 Å) and the approximate point where a next-neighbor graphite layer would have been placed (7.2 Å).

Figure 3

Benzene-graphene (left panel) and naphthalene-graphene (right panel) binding-energy curves. Like that for graphene-graphene, the general geometry vdW-DF calculations (solid lines) give results comparable to experiment (boxes); see text. The two vertical dashed lines mark the minima and the next-neighbor graphite layer, as in Fig. 2.