Mapping Atomistic to Coarse-Grained Polymer Models Using Automatic Simplex Optimization to Fit Structural Properties

We develop coarse-grained force fields for poly(vinyl alcohol) and poly(acrylic acid) oligomers. In both cases, one monomer is mapped onto a coarse-grained bead. The new force fields are designed to match structural properties such as radial distribution functions of various kinds derived by atomistic simulations of these polymers. The mapping is therefore constructed in a way to take into account as much atomistic information as possible. On the technical side, our approach consists of a simplex algorithm which is used to optimize automatically nonbonded parameters as well as bonded parameters. Besides their similar conformation (only the functional side group differs), poly(acrylic acid) was chosen to be in aqueous solution in contrast to a poly(vinyl alcohol) melt. For poly(vinyl alcohol), a nonoptimized bond angle potential turns out to be sufficient in connection with a special, optimized nonbonded potential. No torsional potential has to be applied here. For poly(acrylic acid), we show that each pea...