Adsorption of rare-gas atoms on Cu(111) and Pb(111) surfaces by van der Waals corrected density functional theory

The DFT/vdW-WF method, recently developed to include the Van der Waals interactions in Density Functional Theory (DFT) using the maximally localized Wannier functions, is applied to the study of the adsorption of rare-gas atoms (Ne, Ar, Kr, and Xe) on the Cu(111) and Pb(111) surfaces at three high-symmetry sites. We evaluate the equilibrium binding energies and distances and the induced work-function changes and dipole moments. We find that for Ne, Ar, and Kr on the Cu(111) surface the different adsorption configurations are characterized by very similar binding energies while the favored adsorption site for Xe on Cu(111) is on top of a Cu atom, in agreement with previous theoretical calculations and experimental findings and in common with other close-packed metal surfaces. Instead, the favored site is always the hollow one on the Pb(111) surface, which therefore represents an interesting system where the investigation of high-coordination sites is possible. Moreover, the Pb(111) substrate is subject, upon rare-gas adsorption, to a significantly smaller change in the work function (and to a correspondingly smaller induced dipole moment) than Cu(111). The roles of the chosen reference DFT functional and of different van der Waals corrections as well as their dependence on different rare-gas adatoms are also discussed.

Figure 1

Binding energy of Xe on Cu(111) in the top and hollow configurations using pure PW91 (full and empty circles, respectively) and DFT/vdW-WF (solid and dashed lines, respectively), as a function of the distance $z$ from the surface.

Figure 2

Binding energy of Xe on Pb(111) in the top and hollow configurations using pure PW91 (full and empty circles, respectively) and DFT/vdW-WF (solid and dashed lines, respectively), as a function of the distance $z$ from the surface.

Figure 3

Electron-density difference of Xe on Cu(111) in the (a) hollow and (b) top sites shown in a plane perpendicular to the surface, within the range of $\pm 1\times {10}^{-4}e/{\mathrm{bohr}}^3$. Light gray (red) and dark gray (blue) represent electron accumulation and depletion, respectively. The green and orange spheres indicate the Xe and Cu atoms, respectively.

Figure 4

Electron-density difference of Xe on Pb(111) in the (a) hollow and (b) top sites shown in a plane perpendicular to the surface, within the range of $\pm 1\times {10}^{-4}e/{\mathrm{bohr}}^3$. Light gray (red) and dark gray (blue) represent electron accumulation and depletion, respectively. The green and gray spheres indicate the Xe and Pb atoms, respectively.