Stress relief from alternately buckled dimers in Si(100)

First-principles calculations of the surface stress for the c(4×{}2) buckled-dimer reconstruction of the clean Si(100) surface reveal a significant relief of a compressive contribution to the stress in the direction parallel to the dimer rows, and thus a decrease of the stress anisotropy, when compared to similar calculations for 2×{}1 reconstructions. We show that the mechanism involved is not just the buckling but its alternation along a dimer row. Calculations using the c(4×{}2) model for the clean surface are also in close quantitative agreement with the experimentally measured excess tensile stress of the As-covered surface.