MODIFICATION OF FINNIS-SINCLAIR POTENTIAL TO ACCOUNT FOR SURFACE EFFECT. Z. Kaszkur, Institute of Physical Chemistry PAS, Kasprzaka 44/52, 01-224 Warsaw, Poland

Long range N-body Finnis-Sinclair (F-S) potentials are the example of a simple tight binding approach to describe cohesion in transition and noble metals [1]. This approach applied to fcc transition metals describes satisfactory their elastic properties as well as direction of a surface driven relaxations, contrary to binary, Lennard-Jones type potentials [2]. The simple tight binding scheme is however far from accurate when predicting surface energy and leaves surface tension values underestimated by about 50% in comparison to experimental data. In the present work the surface tension values for 100, 110 and 111 surfaces have been calculated for F-S potentials for palladium evidencing similar discrepancy between the model and experiment. Calculated depth profiles of surface layers displacement show however excellent agreement with the experiment.

The problem of wrong energy estimation in the surface area may be cured by modifying the constant weighting the cohesive part of the simple tight binding potential, making it dependent on the local coordination number, when the interaction is restricted to nearest neighbours only [3]. A similar approach has been applied in this work to the long range F-S potentials after redefining the concept of the coordination number. The results of calculations for single crystal and cluster surface relaxation calculations is presented and discussed.

[1] A.P.Sutton, J.Chen, Phil.Mag.Lett., 61, 139-146 (1990).

[2] V.Rosato, M.Guillope, B.Legrand, Phil.Mag.A, 59, 321-336 (1989).

[3] J.L.Rousset, J.C.Bertolini, P.Miegge, J.Phys.Chem., in print