The
dominant models of polymers, i.e. the freely jointed chain (FJC) model, the wormlike
chain (WLC) model and the freely rotating chain (FRC) model are modified by
integrating the inherent single-molecule elasticity obtained from quantum
mechanics (QM) ab-initio calculations. The QM modified models have been
utilized to generate fitting curves for single-stranded DNA obtained in organic
solvent. The analyses on the deviation between the fitting curve and the
experimental force curve demonstrate that the QM-FRC and QM-FJC model are
suitable for ssDNA, but not the QM-WLC model. We also find that one repeating
unit of ssDNA is corresponding to a Kuhn segment in QM-FJC model or two
rotating units in QM-FRC. Having close correlation to the inherent elasticity
and real molecular structure of the polymer, QM-FJC and QM-FRC are emerging as structure
relevant models.
