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

Abstract

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 closepacked 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 role of the chosen reference DFT functional and of different Van der Waals corrections, and their dependence on different rare-gas adatoms, are also discussed.

Van Der Waals-Corrected Density Functional Theory Simulation of Adsorption Processes on Noble-Metal Surfaces: Xe on Ag(111), Au(111), and Cu(111)

“…Moreover, the adatoms were adsorbed on both sides of the slab: in this way the surface dipole generated by adsorption on the upper surface of the slab is cancelled by the dipole appearing on the lower surface, thus greatly reducing the spurious dipole-dipole interactions between the periodically repeated images (previous DFT-based calculations have shown that these choices are appropriate [9,13,30,63]). …”

“…All calculations have been performed with the Quantum-ESPRESSO ab initio package [58] and the MLWFs have been generated as a post-processing calculation using the WanT package [59]. Similarly to our previous studies [30,33] we modeled the metal surface using a periodically-repeated hexagonal supercell, with a ( √ 3 × √ 3)R30 • structure and a surface slab made of 15 metal atoms distributed over 5 layers considering the experimental Ag(111), Au(111), and Cu(111) lattice constants. Repeated slabs were separated along the direction orthogonal to the surface by a vacuum region of about 20Å to avoid significant spurious interactions due to periodic replicas.…”

“…We have carried out calculations for various separations of the Xe atoms adsorbed on the top high-symmetry site (on the top of a metal atom), since this is certainly the favored adsorption site for Xe [30,[64][65][66][67]. For the Xe-Ag(111) system we have also considered adsorption on the hollow site (on the center of the triangle formed by the 3 surface metal atoms contained in the supercell) in order to verify whether the present schemes are able to correctly predict which configuration is energetically favored (see discussion in ref.…”

“…We have already investigated, by the first version of the approach based on the use of the MLWFs, that is the DFT/vdW-WF method [23,24,37], the adsorption of Xe on the Cu(111) and Pb(111) surfaces [30], however in those applications a more crude description of screening effects in metal substrates was adopted.…”

“…[19][20][21]). We have developed a family of such methods, all based on the generation of the Maximally Localized Wannier Functions (MLWFs) [22], successfully applied to a variety of systems, including small molecules, water clusters, graphite and graphene, water layers interacting with graphite, interfacial water on semiconducting substrates, hydrogenated carbon nanotubes, molecular solids, and the interaction of rare gases and small molecules with metal surfaces [23][24][25][26][27][28][29][30][31][32][33][34][35]. Of a particular value is the possibility of dealing with metal surfaces; in fact insulating surfaces could be somehow treated even using atom-based semiempirical approaches where an approximately derived R −6 term, multiplied by a suitable short-range damping function, is explicitly introduced.…”