MODELS AND EQUILIBRIUM PROPERTIES OF STIFF MOLECULAR CHAINS

The partition functions of discrete as well as continuous stiff molecu lar chains are calculated using the maximum entropy principle. The cha in is described by mass points, and their connectivity is taken into a ccount by harmonic constraints (flexible segments) in addition to the bending restrictions. For comparison and as a test of the formalism th e freely rotating chain as well as the Kratky-Porod wormlike chain (ri gid segments) are reexamined treating the bending restrictions as cons traints. It is shown that the second moments for the chain of flexible segments agree exactly with those known from the freely rotating chai n for the discrete as well as the continuous chain and for all stiffne sses. Moreover, the Green's function for the continuous chain is deter mined, which allows to obtain any desired two point distribution funct ion. The influence of various bending restrictions on equilibrium prop erties is discussed. Furthermore, a comparison to other existing model s, especially the Harris and Hearst model, is given and the validity o f the various models is examined.