Alkali halide surfaces: Adsorbate binding energies and structures at surface defects

We describe an electrostatic method of calculating equilibrium configurations of alkali halide diatomic molecules (monomers) and tetratomic dimers adsorbed on rigid alkali halide crystal surfaces. Results are presented for adsorbate binding energies and geometries on the smooth surface, at single-step ledge defects, and at kink (corner) defects. The results are consistent with our recent experimental measurements and we explore several features of the adsorbate–substrate interaction. Cyclic dimers are more weakly bonded than monomers on the smooth surface, but binding strengths for both are nearly equivalent at ledges. Linear dimers are stabilized at the defect binding sites. For all species, the kink position is the strongest adsorption site. Adsorbate structures at the different sites are dependent on the relative magnitudes of adsorbate–adsorbate and adsorbate–substrate interactions.