Mechanism of thermal destabilization of the Davydov soliton

Following similar work in polaron theory, Davydov has proposed soliton formation and propagation as a mechanism for energy storage and transport in proteins. This paper deals with the energetics of soliton disappearance and is of interest for polaron theory as well. A semiclassical Davydov model is used, for which exact wave functions can be determined. The results in a special case equal those obtained with the full quantum-mechanical model. Monte Carlo simulations show that thermal destabilization is not associated with transitions to exciton states, as is usually assumed in the literature, and that it involves instead disordered states with energies intermediate between those of the minimum energy soliton state and those of the exciton states. At biological temperatures, the Davydov system exhibits ‘‘universal’’ (i.e., parameter independent) behavior.