  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.
