Charge-density-wave formation by Van Hove nesting in the \alpha-phase of   Sn/Ge(111)
  We study the role of electron correlations in the formation of the surface charge-density-wave state in the Sn/Ge(111) interface. The Fermi energy of the overlayer is treated as a dynamical variable, which undergoes a substantial renormalization by the interaction. We show that the Fermi level turns out to be pinned to a Van Hove singularity in the density of states, which explains the formation of the charge-density-wave, the observation of a very flat band in photoemission experiments and the reduction of the spectral weight in the low-temperature phase. 
J. Gonzalez