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

The geometrical and electronic structure of 1/3 monolayer of Sn on the Ge(111) surface is investigated within density functional theory. The well known 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 1U-2D 3 x 3 structure is the more favorable one, not only from an energetic point of view but also from a comparison with STM experiments. On the other hand, the static room temperature electronic band structure of the root 3 x root 3 hardly compares with the available photoemission data, thus supporting the idea of a dynamical flipping of the Sn ad-atoms.