  An extended elastic eigenvector approach had earlier been developed to
interpret ab-initio calculations of adatom interactions. It shows oscillating
interactions as well as trio- and quarto (multisite) terms within clusters. It
is now applied to the interaction of Fe adatoms on Cu(111). The extended
approach differs from previous calculations by using a sharp cutoff -
generating oscillating interactions - and by taking into account interacting
dimers - generating strong anisotropies and multisite terms. Additional weak
anisotropy stems from the substrate and from the surface Brillouin zone shape.
This approach has 3 free parameters which have been fitted to first principles
interactions of Fe adatoms on Cu(111). Elastic adatom pair interactions and
dimer-dimer interactions at mesoscale separations show a reasonable good fit to
the first principles interactions. At smaller separations elastic interaction
values remain questionable. To enable a comparison with future first principle
calculations also dimer-monomer interactions are shown. Some conclusions on
initial adatom formation and diffusion are proposed and open questions are
formulated.
