Rotation of Ge ad-dimers on Ge(0 0 1)

Structural calculations of the Ge ad-dimer rotation on Ge(0 0 1)-2×1 and Ge(0 0 1)-c(4×2) surfaces were performed by ab initio and semiempirical methods. Besides the two (already known) stable adsorption sites on top of the substrate dimer rows (angles between substrate dimer bond and ad-dimer bond are 0° and 90°, respectively) a new local minimum was found. The angle between the substrate dimer bond and the ad-dimer of this local minimum is about 45°. This theoretical result might explain the observation of the so-called A/B Ge ad-dimers on Ge(0 0 1).