Optical and Acoustical Frequencies in a Nonlinear Helicoidal Model of DNA Molecules

We compare optical and acoustical frequencies in the Peyrard--Bishop--Dauxois model, i.e. an extended Peyrard--Bishop model, of DNA molecules. We discuss how ratio of those frequencies depends on a value of the harmonic constant of the helicoidal spring K. Also, we suggest that the most favourable mode could be a resonance mode.