A simple approach to the calculation of surface defect energies in transition metals

In order to understand the energetics of various atomic processes involved in crystal growth, we have developed a simple approach for calculating surface defect energies in transition metals. The total energy of each system is split into two contributions: an attractive term which 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 approximation. Both the pairwise repulsive interaction and the tight-binding hopping integrals are assumed to decrease exponentially when the interatomic distance increases and the equilibrium geometry can be determined from total energy minimization. A few examples aiming at interpreting some field ion microscopy experiments carried out on transition metals will be presented: interaction of an adsorbate with a surface step, relative stability of normal (bulk) and fault (surface) adsorption sites on the close-packed (111) fcc and (0001) hcp surfaces and of islands of adatoms on (111) fcc surfaces.