Absence of large compressive stress on Si(111)

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Abstract
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.