Absence of large compressive stress on Si(111)

The surface stress tensor is calculated from first principles for several Si(111)1×{}1, 2×{}1, and 2×{}2 surfaces. Contrary to widely held expectations, only a weak compressive stress is found for the unreconstructed 1×{}1 surface. Reconstructions involving {π}-bonded chains or adatoms are predicted to be under substantial tensile stress. The results indicate that relief of surface stress is not the driving force for the 7×{}7 reconstruction. The stress is shown to be useful in prediction of the effect of externally applied strain, which can drive changes in the surface reconstruction pattern.