Surface Science 138 (1984) L129-L136 North-Holland, Amsterdam Ll29 SURFACE SCIENCE LEITERS zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPON CALCULATION OF THE STRUCTURAL ENERGY OF THE UNRECONSTRUCTED AND (1 x 2) RECONSTRUCTED Pt(ll0) SURFACE D. TOMANEK, H.-J. BROCKSCH and K.H. BENNEMANN Institut fiir Theoretische Physik, Freie Uniuersitiit Berlin, Arnimollee 14, D 1000 Berlin 33, Fed. Rep. zyxwvutsrq of Germany Received 29 November 1983; accepted for publication 20 December 1983 Describing the binding energy of both d and s valence electrons within the LCAO formalism, and by including repulsive Born-Mayer type interactions, we study the structural stability of the reconstructed and unreconstructed Pt(ll0) surfaces. Our main result is that amongst the various models for the (1 x2) reconstruction the “Bonzel-Ferrer” model is unfavoured, while the “miss- ing-row” model seems to be energetically degenerate with the unreconstructed surface. Our calculation predicts also a small surface concentration, which, however, has only a minor effect on the total energy of the system. It is well established that the (110) surfaces of the late 5d metals Ir, Pt and Au show a (1 X 2) reconstruction at room temperature [l-3]. Various models have been proposed for the atomic arrangement at these surfaces [4,5]: the “paired rows”, the “buckled surface” and the “missing-row” model. Mainly based on a low-energy electron diffraction (LEED) data analysis, the “missing- row” model seems to be favoured at these surfaces [5]. Due to difficulties with regard to explaining the mass transport, Bonzel and Ferrer proposed an alternative sawtooth model [5] for the reconstructed surface. Recent scanning tunnelling microscopy (STM) and X-ray diffraction experiments suggest a disordered surface structure with “missing-row”-like domains [6,7]. In order to clarify the controversy about the equilibrium atomic structure at those fee (llO)-(1 x 2) surfaces, we calculated the total energy for the unrecon- structed as well as for the “missing-row” and the “Bonzel-Ferrer” recon- structed Pt(ll0) surface. The structure models for these surfaces are schemati- cally given as insets in fig. 1. In our calculation, the cohesive energy .&, is given by an attractive band-structure term E,, due to d- and s-electron cohesion, and by a repulsive Born-Mayer type interatomic interaction zyxwvutsrqpon E, mainly due to s-electron repulsion. Thus, E cob =E,s +E,t (1) 0039-6028/84/$03.00 0 Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)