On correlation effects in the indirect interaction between adatoms

Starting from a nonorthogonal basis set a model Hamiltonian for the chemisorption of two adsorbates is derived. The nonorthogonality is converted into a renormalization of the matrix elements. A solution is presented which becomes exact in two limiting cases. The indirect interaction energy of two hydrogen atoms is calculated for adsorption on a semi infinite simple cubic solid described by ans-band. For the band nearly filled (parameters of Ni) a 2 × 2 structure seems to be energetically favourable.