The results were reported of a theoretical study of an adsorbate-induced surface reconstruction. Hydrogen adsorption on a W(100) surface caused a switching transition in the symmetry of the displacements of the W atoms within the ordered c(2 x 2) phase. This transition was modelled by an effective Hamiltonian, where the hydrogen degrees of freedom were integrated out. Based upon extensive Monte Carlo renormalization-group calculations it was shown that the switching transition was of second order at high temperatures and of first order at low temperatures. This behaviour was qualitatively explained in terms of an XY model where there was an interplay between fourfold and eightfold anisotropy fields. The calculated phase diagrams were also compared with a simple mean-field theory.

Theory of Adsorbate-Induced Surface Reconstruction on W(100). K.Kankaala, T.Ala-Nissila, S.C.Ying: Physical Review B, 1993, 47, 2333-43