Monte Carlo test of electrostatic persistence length for short polymers

摘要

A Metropolis Monte Carlo program with reptation is used to generate sample configurations of short electrically charged polymers with thermally distributed Debyendash;Huuml;ckel electrostatic energies. The polymer is a three fold rotational isomeric state model with bond angle thgr; between 5deg; and 90deg; and number of unitsNbetween 10 and 225. To compare the resulting roothyphen;meanhyphen;square (rms) values for radius of gyrationS, and endhyphen;tohyphen;end lengthR, to theory, we use a wormlike chain with contour lengthLequal to the stretched out length of the polymer, the same total charge, and an intrinsic persistence length set so that, for largeN, for specified thgr; andL,Sagrees with the rotational isomeric state model. The results are compared with the predictions forS, with correction for finiteL, of Odijk lsqb;J. Polymer Sci., Polymer Phys. Ed.15, 477 (1977)rsqb;. They are then compared with three attempted corrections for excluded volume: (1) Odijk and Houwaart lsqb;J. Polymer Sci., Polymer Phys. Ed.16, 627 (1978)rsqb;; (2) correction (1) modified by using the electrostatic excluded volume of Fixman and Skolnick lsqb;Macromolecules11, 863 (1978)rsqb;; (3) correction (2) modified by replacing the Yamakawandash;Tanaka formula by an approximation due to Gupta and Forsman lsqb;Macromolecules5, 779 (1972)rsqb;. Odijkrsquo;s prediction with correction for finite length works fairly well under conditions of small excluded volume. The excluded volume corrections are often but not always of about the right size; the latter two work better.