(a) Top view of the surface unit cell for (3 × 3) (black lines), (2 × 2) (blue lines), and (√3 × √3)R30º (red lines); (b) Definition of the height of K atom from the surface, h (Å), and the vertical surface rumpling, δ (Å). The letters “t,” “b,” “f,” and “h” stand for the top, bridge, fcc, and hcp.
The contributions from the bonding energy of K on the deformed Au(111) (ΔE 1), the energy cost of the surface deformation (ΔE 2), and the formation energy of one K atom from isolated gas phase to a K layer (ΔE 3) for K adsorption on Au(111) at ΘK = 0.11 ML, 0.25 ML, and 0.33 ML. Of note, the mesh regions (ΔE 2) are located on the bottom of magenta (ΔE 1) bars to manifest the energy cost of surface deformation.
Charge density difference contours of (a) 0.11 ML K, (b) 0.25 ML K, and (c) 0.33 ML K at hcp site. Contours with warm and cold colors correspond to charge accumulation and depletion, respectively.
Planar averaged charge changes of (a) 0.11 ML K, (b) 0.25 ML K, and (c) 0.33 ML K at hcp site. The average locations of each layer are indicated by the solid circles: smaller ones stand for the Au layers, while the bigger ones indicate the K layers. The height (Z) of surface layer is set to zero.
Possible adsorption configurations for the K–Au intermixed structures. (a) One Au adatom at fcc; (b) two Au adatoms at fcc; (b*) two Au adatoms with one at fcc and the other at hcp; (c) and three Au adatoms at fcc. The (2 × 2) unit cell is shown by the white lines. The letters “t,” “b,” “f,” “h,” and “s” stand for the top, bridge, fcc, hcp, and substitutional sites. The numbers “0,” “1,” “2,” and “3” indicate number of Au adatoms the adsorbed K may bond to. The star “*” is used to distinguish the same type sites with different distances to the adsorbed K atoms. In (b), b2* is a long bridge site between two non-adjacent Au adatoms (blue line). The gold adatoms are marked by the red balls to guide the eye.
Charge density difference contours for the most stable structure of K–Au intermixed layer. The cutting plane is shown in the upper left corner. Contours with warm and cold colors correspond to charge accumulation and depletion, respectively. The structural parameters (unit: Å) are shown correspondingly. The gold adatoms are marked by the red balls to guide eyes.
(a) Surface free energies (γ DFT) as a function of the chemical potential of K (μ K) at ΘK ≤ 0.5 ML on Au(111) with or without Au adatoms. The corresponding scales are shown for 3 selected temperatures. The energetically preferred adsorption configurations at each ΘK (cf. Tables I and II) are shown by the solid lines. (b) Calculated (T, p) phase diagram for K/Au(111) system indicating the stable structures at ΘK = 0.11–0.5 ML.
Adsorption energies, Eads, and structural parameters for K on Au(111) at the coverage of 0.11, 0.25, and 0.33 ML. Heights of K from the surface, h, K–Au bond lengths, d K–Au, effective radii of K, R eff, and surface vertical rumpling, δ, respectively. The adsorption sites are defined in Figs. 1 and 5.
Total energies, E tot(n, m), adsorption energies, E ads, and the energy cost for creating m gold atoms, E cost(m), for K adsorption at 0.25, 0.5 ML on Au(111) with m gold adatoms (m = 0, 1, 2, 3). The unit is electron volt (eV). At each ΘK and ΘAu, only the lowest energy results are listed. The adsorption sites for K are defined in Fig. 5.
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