Mapping atomistic to coarse-grained polymer models using automatic simplex optimization to fit structural properties

摘要

We develop coarse-grained force fields for poly (vinyl alcohol) and poly(acrylic acid) oligomers. In both cases, one monomer is mapped onto acoarse-grained bead. The new force fields are designed to match structuralproperties such as radial distribution functions of various kinds derived byatomistic simulations of these polymers. The mapping is therefore constructedin a way to take into account as much atomistic information as possible. On thetechnical side, our approach consists of a simplex algorithm which is used tooptimize automatically non-bonded 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 non-optimized bond anglepotential turns out to be sufficient in connection with a special, optimizednon-bonded potential. No torsional potential has to be applied here. For poly(acrylic acid), we show that each peak of the radial distribution function isusually dominated by some specific model parameter(s). Optimization of the bondangle parameters is essential. The coarse-grained forcefield reproduces theradius of gyration of the atomistic model. As a first application, we use theforce field to simulate longer chains and compare the hydrodynamic radius withexperimental data.