Competition between reduced delocalization and charge transfer effects   for a two-band Hubbard model
  We use the embedding approach for a dynamical mean-field method to investigate the electronic properties of a semi-infinite two band Hubbard model at half- and quarter-filling. Two effects determine the degree of correlation at the surface: first, there will charge transfer between the surface and the bulk, and, secondly, electrons at the surface are less delocalized due to the reduced coordination number. We determine the result of these two effects and compute the quasiparticle weight. It is shown that depletion of charge from the surface to the bulk at quarter-filling competes with enhanced correlation effects; the net result is that at quarter-filling the quasi particle weight at the surface is approximately equal to the bulk quasi particle weight. Only when the charge transfer approaches zero at large interaction strengths does the quasi particle weight at the surface become lower than that in the bulk. 
Reza Nourafkan and Frank Marsiglio
cond-mat.str-el