Visualization of tight-binding calculations - The electronic structure and electron localization of the Si(100) surface

The advantage of computer graphics in the visualization of tight-binding calculations is highlighted in a model study of the reconstruction of the Si(100) surface. Three different surface models-the unreconstructed surface Si(100)-(1 x 1), and symmetric and asymmetric pairing of surface atoms Si(100)-(2 x 1)-are investigated on the basis of density of states (DOS), local (projected) density of stales (LDOS) and crystal orbital-overlap population (COOP) analysis. For the visualization of the real-space properties of tight-binding calculations, two- and three-dimensional images of the total (TED) and partial electron densities (PED) are shown. The PED calculated near the Fermi level are compared to densities of HOMOs and LUMOs in molecular systems and used to analyse constant current mode STM images, obtained by applying bias voltages of different sign. They shaw excellent agreement with STM experiments. The electron-localization function (ELF) has been shown to describe chemical bonds in molecules and solids surprisingly well. Here, the ELF is calculated for surfaces. In order to visualize the shape of the ''dangling'' surface bonds and bonds connecting surface atoms, two- and three-dimensional representations of the ELF are discussed. Using the reconstruction of the Si(100) surface as an example, we show that combining methods for extracting information from quantum mechanical calculations, such as PED, TED and ELF, leads to a more comprehensive description of the electronic surface structure. With the help of computer graphics, chemical concepts routinely used for describing local properties of molecules can be transferred very effectively to extended systems.