Adsorption of ${\mathrm{C}}_{60}$ on Au(111) revisited: A van der Waals density functional study

We address the dispersion force in a ${\mathrm{C}}_{60}$/Au(111) interface using the van der Waals density functional with improved exchange [V. R. Cooper, Phys. Rev. B 81, 161104(R) (2010)] and nonlocal correlation [K. Lee, É. D. Murray,L. Kong, B. I. Lundqvist, and D. C. Langreth, Phys. Rev. B 82, 081101(R) (2010)]. We found that the adsorption is solely attributed to the nonlocal correlation, i.e., the van der Waals (vdW) forces, and the correct account of vdW attraction between ${\mathrm{C}}_{60}$ molecules is also essential to obtain accurate binding energy. The bonding of ${\mathrm{C}}_{60}$ is, however, covalent-like, which is originated from the hybridization of the lowest unoccupied molecular orbital of ${\mathrm{C}}_{60}$, in agreement with a previous theoretical study.

Figure 1

Top view of adsorption geometry of ${\mathrm{C}}_{60}$ at an fcc-hollow site of Au(111). The unit cell used is indicated by the parallelogram.

Figure 2

Interaction energy of ${\mathrm{C}}_{60}$ with Au substrate on a fcc-hollow site as a function of ${\mathrm{C}}_{60}$-Au distance obtained using different exchange-correlation functionals. The distance is indicated by the arrow in the inset. The molecule-molecule interaction energy is not included.

Figure 3

(a) Isosurface of the differential charge between ${\mathrm{C}}_{60}$ and Au substrate. White (light) surfaces indicate accumulated charge, while blue (dark) surfaces indicate depleted charge. The isovalue is 1.350 $e$/nm${}^3$. (b) PDOSs onto HOMOs and LUMOs, and (c) corresponding COOPs.