Deformation of semiflexible chains

The force-extension relation and the end-to-end distribution function are calculated in the constant force and constant extension ensemble, respectively, for a semiflexible chain of Gaussian segments. Qualitative differences are found for these quantities when the persistence length is on the order of the chain length. In particular, beyond a certain persistence length, the free energy assumes two extreme values in the constant extension ensemble corresponding to zero force at zero and at a finite extension. The comparison of the force-extension relation with experimental results on DNA exhibits excellent agreement. The approach provides a simple expression for the end-to-end distribution function which is in excellent agreement with Monte Carlo simulations of the Kratky-Porod semiflexible chain model. (C) 2003 American Institute of Physics.