Ge-dimer relaxation on Si(100)

We employ ab initio total-energy-minimization techniques to study the relaxation of Ge dimers on Si(100). We find that the dimers adopt an asymmetric configuration, in agreement with recent experimental results [E. Fontes et al., Phys. Rev. Lett. 70, 2790 (1993)]. The average dimer height displacement and tilting angle are found to be 0.79 \AA{} and +19\ifmmode^\circ\else\textdegree\fi{}, respectively. Our calculations predict that the (2\ifmmode\times\else\texttimes\fi{}2) and c(4\ifmmode\times\else\texttimes\fi{}4) reconstructed structures have the same energy, and suggest that either one of these two could be the ground-state structure.