Electron correlation effects in the Si (111)-5 × 5 and -7 × 7 surfaces

LDA-calculations have been performed for determining the electronic properties and the surface band structure of the Si (111)-5 × 5 surface. The six narrow surface bands that appear around the Fermi energy are essentially related with the six adatoms dangling bonds, and contain 3 electrons. From these calculations, a two-dimensional model is introduced to describe the electron correlation properties of those narrow bands. These results are compared with the ones published elsewhere for the Si(111)-7 × 7 surface. Our analysis shows that the Si (111)-5 × 5 surface has a semiconducting character while the Si (111)-7 × 7 reconstruction presents a metallic behaviour. Both surfaces exhibit important correlation effects that arise from the localization of electrons on some elementary structures having a hexagonal ring geometry.