Calculation of Lattice-Gas Parameters by Density Functional Theory

CALCULATION OF LATTICE-GAS PARAMETERS BY DENSITY FUNCTIONAL THEORY 

There are many methods to estimate LG parameters. One of these is comparison of MC simulations (see Sect. V) of a LG model with experimental adsorption isotherms. For detailed descriptions of this method we refer to Refs. [30,31,36-39]. Here we instead concentrate on the purely theoretical method based on quantum-mechanical DFT calculations.  

DFT is the most widely used method to calculate ground-state properties of many-electron systems. It is based on the Hohenberg-Kohn theorem, which states that all properties of the many-particle ground state can be expressed in terms of the ground-state electron 

Here we present preliminary results on a DFT calculation of lateral interaction constants pertaining to a LG model for the adsorption of Br on single-crystal Ag(lOO) surfaces. The LG model is represented by (3) on a square lattice with lattice constant a = 2.95 A, Tfs = 0, infinitely repulsive interactions for adparticles at nearest-neighbor sites, and the long-range repulsion 

We prepared slabs with seven metal layers, which were placed inside a supercell with periodic boundary conditions. Two different sizes of supercells were used a 2 x 2 supercell with size of 2a x 2a x 36.95 A, and a 3 x 3 supercell with size of 3a x 3a x 36.95 A. The vacuum region above the surface was twice the thickness of the slab, and the orientation of the surface normal was in the z direction. One, two, and three Br atoms were placed on the 3 x 3 surface to represent coverages = 1/9, 2/9, and 1/3. Two Br atoms were placed on the 2x2 surface to represent = 1 /2, and one Br atom was placed on the 2 X 2 surface to represent = 1 /4. Supercells with different coverages of Br are shown in Fig. 3. 

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