Slab model, platinum surface

FIG 3 (a) A slab model of the platinum (111) surface, consisting of 12 atoms. The symmetry of the supercell is hexagonal, (b) Two hundred fifty-six supereells. 

A simple test of this suggestion is the comparison of a five-layer slab calculation for the Knight shift in platinum (70) with the spectral fits of the layer model (Fig. 48). In both cases the surface resonance is shifted about 4% to low field wuth respect to the bulk signal, and the subsurface signal is found at approximately the halfway point. Another test is qualitatively to compare experimental results for hydrogen chemisorption on platinum (Fig. 55) with a calculation for hydrogen on palladium (175) in both cases an important diminution of the surface LDOS on the metal is found. 

As the last example we discuss the recent study of Skiilason et al. who examined the hydrogen evolution at a platinum electrode. They studied the model system of Fig. 22 that contains a slab of Pt atoms, representing the Pt(lll) surface. On top of that, two layers of water molecules plus an excess of H atoms are placed. Thereby, protons become solvated in the water, leading to the formation of ions,... 

Geometry optimizations were performed on a super-cell structure using periodic boundary conditions. The (111) surfaces were generally modeled using a 3 x 2 /3 super cell. The metal slab was chosen to be three atomic layers thick, and a 15 A vacuum layer was used to ensure that there were no interactions between the surface adsorbates on one layer and the next slab. The first metal layer was allowed to relax, while the bottom two layers of the platinum atoms were held fixed in their bulk position. All atomic coordinates of the adsorbed species and the metal atoms in the relaxed metal layers were optimized to a force of less than 0.025 eV A-1 on each atom. 

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