First principles calculations of the cleaved and annealed Ge(111) surfaces

We use ab initio molecular dynamics to study the structural and electronic properties of cleaved and annealed Ge(111) surfaces. New features emerge for both structures. For the (2 × 1) it is found that even though the stable state has a π-bonded chain structure, there are two isomers with the tilt angle of the chain in opposite directions. For the c(2 × 8) we find an asymmetry in the surface unit cell, in agreement with LEED experiments that show weak quarter-order spots. This inequivalence also produces a splitting of the rest atom and adatom dangling bond, which explains recent STM experiments.