Stress and reconstruction on (0 0 1) transition-metal surfaces

We investigate the role of surface stress in the hex reconstruction of (0 0 1) transition-metal surfaces introducing the density-functional-theory stress density, a theoretical tool allowing the local analysis of the stress. By ab initio total energy, stress, and stress density calculations for Ir (0 0 1) we show that the reconstruction is due to the concurrence of tensile stress relief in the surface layer and the huge outward relaxation thereof. The latter causes a compressive stress relief in the region between the surface layer and the substrate, leading to an increased total surface stress.