The unit cell used for the adsorption of O. Sites for 0.25 coverage are designated “1,” while additional sites for 0.5 coverage are designated “2.” Abbreviations are for bridge, for hollow, and for top.
The unit cell for the surface. There are six surface atoms on top of five second-layer atoms.
The supercell for our larger calculations. The letter designate the adsorption sites for the straight configuration, while the letter represents the staggered adsorption sites.
Side view of the calculated slab. Four layers were used. The bottom layer was fixed in bulk positions. designates the vertical distance between layers two and three with being the average distance, while being the minimum distance between atoms in the respective planes. designates the vertical distance between atoms two and three. Atoms three and five are symmetrically equivalent, as are atoms two and six.
Top view of the unit cell of the surface. Hex adsorption positions are identified by the numbering scheme shown. Sites above the numbered sites are not identified, as they are symmetrically equivalent to the identified sites.
Top view of the unit cell of the surface. Top and bridge adsorption positions are identified by the numbering scheme shown. Sites can be identified as top-1, top-2, bridge-1, bridge-2, diagonal-bridge-1, diagonal-bridge-2, etc.
Surface energy for the system at 0 K as a function of oxygen coverage. Results show that the surface at 0.3 coverage is the most stable surface.
Surface energy for the system at 0 K as a function of oxygen coverage. Results show that the surface at 0.6 coverage is the most stable surface.
Phase diagram of the system. The phase with the lowest surface Gibbs free energy at any given temperature is the most stable. Oxygen coverages of 0, 0.1, and 0.3 are shown on the two surfaces. Results show oxygen desorption near 730 K.
Experimental oxygen desorption data from surface. Oxygen was adsorbed at 573 K. exposure was at 0.6 Pa s. Adapted from Ref. 13.
Calculated vertical distances for the and slabs. Distance definitions are given in Fig. 4. Experimental results from LEED for Ir are also shown.
Adsorption energies for O on in . The unit cell in Fig. 1 was used, except for the coverages, which used the unit cell size in Fig. 2, but with a surface. GGA denotugeneralized gradient approximation and LDA denotes local density approximation.
Atomic O adsorption energies on at various adsorption sites in . adsorption energies are also given.
Calculated average distances of bonding Pt atoms and O on and . The O atom in the hex sites binds to three Pt atoms, in bridge sites binds to two Pt atoms, and in top sites binds to one Pt atom. values are also given.
Adsorption energies in . Coverages at and are over the larger supercell (see Fig. 3), while coverages at and are over the smaller cell (see Fig. 2).
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