Reconstruction mechanism of fcc transition metal (001) surfaces

Ab initio studies of the reconstruction mechanism of (001) fcc transition metal surfaces are presented, showing that a close-packed quasihexagonal reconstruction is possible for the late 5d metals Ir, Pt, and Au, while it is disfavored in the isovalent 4d metals Rh, Pd, and Ag. The driving mechanism is identified in the tensile excess stress of the unreconstructed surfaces. The stress overcomes the substrate resistance to reconstruction only in 5d metals, where it is much larger than in 4d metals because of the stronger relativistic effects. The origin of surface stress is a d charge depletion from the surface layer.