Different calculations of the electronic structure of this system have been unable to explain satisfactorily some puzzling features of the experimental surface band structure measured by angle-resolved photoemission (namely, the absence of any adsorbate structure near the Fermi level and the extremely small dispersion of all the adsorbate bands). Here we present a new calculation based on the lattice Anderson model in the (adsorbate) low-density regime. The one-electron Green function is computed directly from its Lehmann representation in terms of N-1 and N+1 electron states. These are obtained approximately with a new configuration interaction approach supplemented by renormalization group techniques in order to include iteratively states with an increasing number of electron–hole pairs. The resulting spectral function is in quantitative agreement with the photoemission spectrum: (1) all the adsorbate features lie between 5 and 10 eV below the Fermi level and (2) the adsorbate band dispersion is small (less than 0.5 eV). We also compare with the random phase approximation.