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

A Density Functional Theory calculation of the geometrical and electronic structure of the a-phase of Sn/Ge(111) surface is presented. The 3×3 and √3 × √3 reconstructions are studied in details, performing also band structure calculations and simulating STM images. Our results confirm that the l U-2D 3×3 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 √3 × √3 surface, instead, hardly compares with the available photoemission data, thus supporting the idea of a dynamical flipping at room temperature of the Sn adatoms.