A SIMPLE APPROACH TO THE CALCULATION OF SURFACE DEFECT ENERGIES IN TRANSITION-METALS

In order to understand the energetics of various atomic processes invo lved in crystal growth, we have developed a simple approach for calcul ating surface defect energies in transition metals. The total energy o f each system is split into two contributions: an attractive term whic h is due to the broadening of d atomic levels (band contribution) and a repulsive one written as a sum of pairwise interactions (Born-Mayer potential). The band contribution is calculated in the tight-binding a pproximation. Both the pairwise repulsive interaction and the tight-bi nding hopping integrals are assumed to decrease exponentially when the interatomic distance increases and the equilibrium geometry can be de termined from total energy minimization. A few examples aiming at inte rpreting some field ion microscopy experiments carried out on transiti on metals will be presented: interaction of an adsorbate with a surfac e step, relative stability of normal (bulk) and fault (surface) adsorp tion sites on the close-packed (111) fee and (0001) hcp surfaces and o f islands of adatoms on (111) fee surfaces.