Large-radius Holstein polaron and the problem of spontaneous symmetry   breaking
  A translation-invariant solution is found for a large-radius Holstein polaron whose energy in the strong coupling limit is lower than that obtained by Holstein. The wave function corresponding to this solution is delocalized. A conclusion is made about the absence of a spontaneous symmetry breaking in the quantum system discussed. 
V.D. Lakhno
cond-mat.other cond-mat.str-el