A theoretical case study:: the Sn/Ge(111)-(3 x 3) surface

We present a theoretical analysis of the Sn/Ge(111)-(3 x 3) surface. The (3 x 3) atomic Structure is searched using a combination of local-orbital and plane-wave density functional methods. We find a ground state geometry that presents two different types of Sn adatoms whose vertical positions differ by similar to 0.3 Angstrom. The electronic structure of the surface is analysed including electron correlation effects. The comparison with recent experimental studies, both on the atomic and electronic structure of this surface, gives a strong support to the structural model presented in this work.