Correlation effects in photoemission spectroscopy: Cl/Si(100)-(2x1)

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.