Potential energy of an isolated gold atom on the (100) surface of alkali halide crystals

The energy of an isolated gold atom on the (100) surface of several alkali halide crystals (NaCl, NaF, KCl, KBr) is calculated as a function of distance above the crystal surface. The calculations include dispersion, electrostatic and repulsive potentials and are performed by direct summation over near neighbours and integration over the rest of the crystal. Detailed potential maps of the (100) surface as seen by a gold adatom are obtained, preferred adsorption sites are identified, and surface quantities such as adsorption energies, minimum energy barriers for diffusion and vibrational frequencies are computed. The effects of relaxations of the (100) surface ions due to both the presence of the surface and the presence of the adatom are examined. Both are found to be significant. Some comparison with experimental results is made.