Density of surface states of ordered adlayers

A method for calculating Green functions has been obtained by extending the continued fraction expansion method. It is applicable to a quasi-tridiagonal hamiltonian. The surface density of states of ordered adlayers has been studied by this method within the tight-binding approximation. Local densities of states of the outermost and the following few atomic planes are calculated for the (2 × 1) and (1 × 2) overlayer on a simple cubic (110) surface. It is found that the effect of long range order of the overlayer and of adsorption site is very important for the electronic structure of the adlayer. The nonbonding state, a new kind of surface state characteristic of the ordered adlayer, is obtained. It is shown that the energy of the nonbonding state degenerates at the orbital energy of an adatom when the direct interaction between adatoms is negligible, so that the states provide a strong peak in the adsorbate band for certain overlayer structures.