Surface Science 152/153 (1985) 155-161 North-Holland, Amsterdam 155 zyxwvutsrqp MULTILAYER RELAXATION AND MELTING OF A METAL SURFACE * C.S. JAYANTHI **, E. TOSATTI and A. FASOLINO International Schoolfor Advanced Studies, Trieste, Italy and L. PIETRONERO Solid State Physics Laborafory, University of Groningen, Melkweg I, 9718 EP Groningen. The Netherlands Received 13 April 1984; accepted for publication 6 June 1984 The effect of multilayer relaxation on melting is investigated here for a high cohesion metal like copper. The method involves finding the quasi-harmonic instability of (100). (110) and (111) surfaces of copper, where the electronic cohesive force is incorporated in a phenomenological way. It is seen that surface contraction has drastic effect on melting making a loose-packed surface melt later than a close-packed one. 1. Introduction Recent room temperature studies of low energy electron diffraction (LEED) and high energy ion scattering (HEIS) predict multilayer relaxation of metal surfaces [1,2]. The first-second layer distance (d,,) is found to be contracted relative to the bulk interplanar spacing while the second-third layer distance (Az3) is found to exhibit the opposite behaviour. The surface contraction (Ad12) in metals has been described to arise from non-pairwise electronic cohesive forces [3,4]. Earlier theoretical models [5,6] based on pairwise poten- tial failed to predict this, as they considered only the effect of depletion of neighbours, neglecting the change of conduction electron density near the surface of metals. In such models, one obtained instead an outward relaxation for the surface layer. For rare gas crystals, these models may still be applicable. * Work supported by GNSM-CNR and by the Italian Minister0 della Pubblica Istruzione. ** Present address: DHPG/SPAS, CEN Saclay, F-91191 Gif-sur-Yvette, France. 0039-6028/85/$03.30 0 Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)