Lang-Firsov approaches to polaron physics: From variational methods to   unbiased quantum Monte Carlo simulations
  We review variational and quantum Monte Carlo approaches based on (extended) Lang-Firsov transformations of the Hamiltonian. Derivations for one, two and many electrons are given, and results for the Holstein polaron, the Holstein-Hubbard bipolaron, and the spinless Holstein model at finite carrier densities are presented. 
Martin Hohenadler, Wolfgang von der Linden