Semiflexible polymers: dependence on ensemble and boundary orientations.

We show that the mechanical properties of a worm-like-chain (WLC) polymer, of contour length L and persistence length lambda such that t=L/lambda approximately O(1), depend both on the ensemble and the constraint on end orientations. In the Helmholtz ensemble, multiple minima in the free energy near t=4 persists for all kinds of orientational boundary conditions. The qualitative features of projected probability distribution of end-to-end vector depend crucially on the embedding dimensions. A mapping of the WLC model, to a quantum particle moving on the surface of a unit sphere, is used to obtain the statistical and mechanical properties of the polymer under various boundary conditions and ensembles. The results show excellent agreement with Monte Carlo simulations.