Dynamic buckling of Si tetramers on the Si(111)-7x7

The atomic structure of Si tetramers that form on the Si$(111)\text{-}7\times 7$ surface during homoepitaxy, is investigated by means of first principles calculations with the currently available atomistic model as starting point. It is demonstrated that the rectangular shape of the Si tetramer is unstable against buckling. Comparison of calculated results with available scanning tunnelling microscopy (STM) data provides a new understanding of the problem, indicating that the recorded STM images are influenced by dynamic buckling.