Oxygen Overlayers on Pd(111) Studied by Density Functional Theory

Abstract

By use of density-functional theory we analyze the on-surface adsorption of oxygen on Pd(111) for coverages up to 1 monolayer and compare the results with corresponding data for the other late 4d transition metals, namely, Ru, Rh, and Ag. Besides the known effect of the continued d-band filling on the oxygen-metal bond strength, we also discern trends in the adsorption geometries, work functions, and electron density of states. The repulsive lateral interactions in the overlayer give rise to a pronounced reduction of the adsorption energy at higher on-surface coverages. In fact, for oxygen coverages θ > 0.5 monolayers, the thermodynamic equilibrium phase of O/Pd(111) is known to be a surface oxide. The calculations reported in this paper show that on-surface adlayers at such higher coverages, that may exist as metastable phases, still possess qualitatively the same surface chemical bond as that which is found at low coverages. The dependence of the surface relaxation on oxygen coverage exhibits some unexpected behavior.

Density-functional theory investigation of oxygen adsorption atPd(11N)vicinal surfaces(N=3,5

“…Geometric structure Using the Murnaghan equation of state, we compute the DFT-GGA-PBE lattice constant for Pd as a = 3.947Å (neglecting zero-point vibrations) and the bulk modulus as B = 157 GPa. These results are in excellent agreement with our previous study using the earlier WIEN97 LAPW code, which gave a = 3.944Å and B = 163 GPa, respectively 11 . The slight overestimation of the lattice constant (about +2% compared to the experimental value of a exp = 3.89Å 12 ) and the (corresponding) underestimation of the bulk modulus (B exp = 181 GPa 12 ) are in line with analogous studies for other late 4d TMs.…”

“…In the shown LDOS for the (1 × 1) overlayer, the bonding states show some substructure due the presence of a noticeable oxygen-oxygen interaction along the rows in the short direction of the surface unit-cell. This leads to the formation of an adsorbate band structure as previously discussed for high-coverage O overlayers at the low-index Pd(111) surface 11 . The surface layers corresponding to atoms not belonging to the immediate NN shell of the oxygen adsorbate show only insignificant variations in the LDOS compared to the case of the clean surface, as does the LDOS in the deeper layers.…”

Interactions of oxygen and hydrogen on Pd(111) surface

“…We find that such contributions can be neglected due to their small values. The adsorption and electronic properties of hydrogen on Pd(111) have been studied by DFT methods in the past [34], showing stable adsorption at hollow fcc sites, with hollow hcp site being less stable [35]. Here, the relaxed hydrogen to Pd atom distance is found to be 1.84 Å, which corresponds to a height of about 0.91 Å.…”

The electronic structure and phase diagram of chlorine adsorption on Mg (0001) surface

“…The hybridization between Cl 3p orbital and Mg 3s orbital cause the band of isolated Cl atom broaden, further form bonding state and anti-bonding state from À7 eV to Fermi level, as shown in Fig. 5(b), the difference between the DOS of the clean and the adsorbate-covered surfaces (DN, which DN > 0 means bonding states) mentioned by Todorova et al [24] clearly reveal the Cl-Mg bonding and anti-bonding states. The bonding state is mostly occupied by electrons, indicating that the interaction between Cl and Mg atoms is stronger and the adsorption energy of Cl adsorption in fcc-hollow is 4.18 eV.…”