Surface structure and energy bands of 1/3ML Sn/Ge(111)

A Density Functional Theory calculation of the geometrical and electronic structure of the alpha-phase of Sn/Ge(111) surface is presented. The 3 x 3 and root 3 x root 3 reconstructions are studied in details, performing also band structure calculations and simulating STM images. Our results confirm that the IU-2D 3 x 3 structure is the more favorable one, from an energetic point of view but also from a comparison with the available photoemission and STM experiments. The electronic band structure of the flat root 3 x root 3 Surface, instead, hardly compares with the available photoemission data, thus supporting the idea of a dynamical flipping at room temperature of the Sit adatoms.