Simulation of a surface - The Slab Model (from a thesis)
From the thesis " Shockley surface states
calculated within
density functional theory "
Page 39
For studying a surface the ideal model would be a semi-infinite crystal extending infinitely in two dimensions x and y and semi-infinitely along the surface normal direction z. With this approach one would only consider the two-dimensional periodicity of the system and ignoring the third dimension. But in practice it is common to use codes which apply periodicity in all three dimensions by using the slabmodel for a surface. To do this one creates a supercell (see figure 3.2) which is repeated in all three dimensions. Only a part of the supercell is filled with atoms whose repetition in the x and y-direction creates the infinite slice of material. The other part of the supercell is empty and simulates the vacuum for the surface. Repeating the supercell in the z-direction creates slab-vacuum-repetitions. It is important that the vacuum is big enough to avoid interactions between the slabs since if the slabs are too close to each other the electron densities are not tailing off to zero in the vacuum and take effect on the neighboring slabs. A supercell of this kind defines two surfaces, one on the upper side and one on the lower side of the slab.
To download the thesis click on the link below:
http://physik.uni-graz.at/~pep/Theses/MasterThesis_Kollmann_Bernd_02_12_2014.pdf
Page 39
For studying a surface the ideal model would be a semi-infinite crystal extending infinitely in two dimensions x and y and semi-infinitely along the surface normal direction z. With this approach one would only consider the two-dimensional periodicity of the system and ignoring the third dimension. But in practice it is common to use codes which apply periodicity in all three dimensions by using the slabmodel for a surface. To do this one creates a supercell (see figure 3.2) which is repeated in all three dimensions. Only a part of the supercell is filled with atoms whose repetition in the x and y-direction creates the infinite slice of material. The other part of the supercell is empty and simulates the vacuum for the surface. Repeating the supercell in the z-direction creates slab-vacuum-repetitions. It is important that the vacuum is big enough to avoid interactions between the slabs since if the slabs are too close to each other the electron densities are not tailing off to zero in the vacuum and take effect on the neighboring slabs. A supercell of this kind defines two surfaces, one on the upper side and one on the lower side of the slab.
To download the thesis click on the link below:
http://physik.uni-graz.at/~pep/Theses/MasterThesis_Kollmann_Bernd_02_12_2014.pdf
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