We show that the conclusion on the breakdown of the standard small polaron theory made recently by E. V. de Mello and J. Ranninger [Phys. Rev. B 55, 14 872 (1997)] is a result of an incorrect interpretation of the electronic and vibronic energy levels of the two-site Holstein model. The small polaron theory, when properly applied, agrees well with the numerical results of these authors. Also we show that their attempt to connect the properties of the calculated correlation functions with the features of the intersite electron hopping is unsuccessful.

• Received 4 September 1997

DOI:https://doi.org/10.1103/PhysRevB.59.12132