The stability of fcc (1 1 1) metal surfaces

The results of a theoretical study on the stability of fcc (1 1 1) metal surfaces to certain commensurate-incommensurate reconstructive phase transformations is presented. Specifically, we have performed computer simulation studies of the 22 × √3 surface reconstruction of Au(1 1 1). This reconstruction involves a uniaxial contraction of the top monolayer corresponding to a surface strain of about 4.3% and has been observed to be the stable structure for the clean surface at low temperatures. The driving force for the reconstruction has been associated with the quantity (f - γ), where f is the surface stress and γ is the surface free energy, while the opposing force is due to the disregistry with the underlying lattice. A continuum model yields a stability criterion that depends on the knowledge of a small number of physical quantities: f, γ, the equilibrium nearest-neighbor spacing r₁ and the shear modulus G. We have performed molecular dynamics simulations as a general stability analysis of these types of reconstructions. The results are in excellent agreement with the continuum model. The simulations using embedded-atom method potentials also accurately reproduce many observed features of the reconstruction on Au(1 1 1).