Jeckelmann E, Fehske H, Exact numerical methods for electron-phonon problems, cond-mat/0510637
Fehske H, Jeckelmann E, Quantum phase transition in one-dimensional electron-phonon systems, cond-mat/0510741
Proville L, Aubry S, Many-polaron states in the Holstein-Hubbard model, JSP 106, 1185 (2002)