Determination of corrugation and friction of Cu(111) toward adsorption and motion of Ne and Xe

The corrugation feature of potential energy surfaces (PESs) for rare-gas (RG) adlayers on metal surfaces has been extensively explored in the positive adsorption energy part. Here, we show that opposite corrugation features may also happen in the negative adsorption energy side for Ne and Xe on Cu(111). While the PES of Ne/Cu(111) is corrugated near the equilibrium adsorption geometry, i.e., Ne prefers the hollow site, the PES of Xe/Cu(111) is anticorrugated, i.e., Xe prefers the atop site. The weak hybridization of RG $p$ and Cu $d$ states is critical for this qualitative difference. Furthermore, the calculated activation energies indicate that Ne may move on Cu(111) at a very low temperature, whereas Xe motion can be activated only above 35 K. We found that the inclusion of the nonlocal van der Waals correction is essential for the correct determination of adsorption and motion energetics for RG adatoms on metals through density functional calculations.

Figure 1

The top and side views of the atomic model adopted in the present calculations. Parallelogram in (a) shows the $\sqrt{3}\times \sqrt{3}$ unit cell, and the arrows 1 and 2 represent the two paths of RG sliding. The T, B, H, and F are for atop, bridge, hcp hollow, and fcc hollow sites, respectively. The large, medium, and small spheres are for the surface, subsurface, and third-layer Cu atoms, and notations $d_{\mathrm{RG}\text{−}\mathrm{Cu}\left(111\right)}$ and $d_{12}$ are marked for the convenience of discussions.

Figure 2

The position and distance dependent adsorption energies of Ne (solid symbols) and Xe (open symbols) on Cu(111). Squares and circles are for energies of RG adatoms on hollow and top sites, respectively. The solid and dashed lines are for eye-guiding purposes. (b) and (c) show the zoom-in plots at the negative and positive adsorption energy regions, as highlighted by the arrows in (a).

Figure 3

Partial density of states (PDOS) of Ne (green dashed lines), Xe (red/light gray), and the metal atom (black) in the topmost layer of (a) Cu (111) and (b) Pb(111). The insets in (a) display the projected $p$ states of Xe around −4.0 eV (left) and +5.0 eV (right) in Xe/Cu(111). The inset in (b) shows the Xe $p$ state around −4.7 eV in Xe/Pb(111). The vertical lines indicate the position of the Fermi level.

Figure 4

The changes of $E_{\mathrm{ad}}$ along (a) path 1 and (b) path 2 shown in Fig. 1: Solid red circles show results for Ne/Cu(111), and open black circles are for Xe/Cu(111). The red and black dashed curves give the LDA results of Ne/Cu(111) and Xe/Cu(111), respectively.