Adsorption of Cu and Ag atoms on Si(111) surfaces: Local density functional determination of geometries and electronic structures

The electronic structures, adsorption geometries, chemisorption energies, and vibrational frequencies of single Cu and Ag atoms on Si(111) surfaces are determined by self‐consistent total energy calculations using first principles, local density functional theory, with a numerical basis for a cluster of 20 Si atoms. The binding energy results reveal that both Cu and Ag adsorb in threefold hollow sites with equilibrium heights of 0.74 A (Cu) and 1.48 A (Ag) above the plane of the surface Si atoms. The adsorption energies are found to be 92 kcal/mol for Cu and 72 kcal/mol for Ag. Assuming a rigid substrate, the calculated frequencies of the perpendicular vibrational modes are 58 cm−1 for Cu and 90 cm−1 for Ag. The lateral diffusion barriers, assuming an unreconstructed rigid Si(111) surface, are found to be 12 and 8 kcal/mol for Cu and Ag, respectively. Calculations for Cu and Ag atoms being moved towards the interior of the cluster, including geometric relaxation of the nearest‐neighbor Si atoms, demonstra...