Vibron Self--trapped States in Biological Macromolecules: Comparison of   Different Theoretical Approaches
  A study of the applicability of the variational treatments based on using of the modified Lang-Firsov unitary transformation (MLF method) in the investigation of the vibron self-trapped states in biological macromolecular chains are presented. We compare the values of the ground state energy predicted by MLF methods with the values of the ground state energy predicted by the standard small-polaron theory, for various values of the basic energy parameters of the system. We obtain regions in system parameter space where MLF approach gives better description of the vibron states. 
D. Cevizovic, S. Galovic, A. Reshetnyak and Z. Ivic
cond-mat.mes-hall physics.chem-ph