Transferability of coarse-grained force fields: the polymer case.

A key question for all coarse-graining methodologies is the degree of transferability of the resulting force field between various systems and thermodynamic conditions. Here we present a detailed study of the transferability over different thermodynamic states of a coarse-grained (CG) force field developed using the iterative Boltzmann inversion method. The force field is optimized against distribution functions obtained from atomistic simulations. We analyze the polymer case by investigating the bulk of polystyrene and polyamide-6,6 whose coarse-grained models differ in the chain length and in the number of atoms lumped in one bead. The effect of temperature and pressure on static, dynamic, and thermodynamic properties is tested by comparing systematically the coarse-grain results with the atomistic ones. We find that the CG model describing the polystyrene is transferable only in a narrow range of temperature and it fails in describing the change of the bulk density when temperature is 80 K lower than the optimization one. Moreover the calculation of the self-diffusion coefficient shows that the CG model is characterized by a faster dynamics than the atomistic one and that it overestimates the isothermal compressibility. On the contrary, the polyamide-6,6 CG model turns out to be fully transferable between different thermodynamic conditions. The transferability is checked by changing either the temperature or the pressure of the simulation. We find that, in this case, the CG model is able to follow all the intra- and interstructural rearrangements caused by the temperature changes. In addition, while at low temperature the difference between the CG and atomistic dynamics is remarkable due to the presence of hydrogen bonds in the atomistic systems, for high temperatures, the speedup of the CG dynamics is strongly reduced, leading to a CG diffusion coefficient only six times bigger than the atomistic one. Moreover, the isothermal compressibility calculated at different temperatures agrees very well with the experimental one. We find that the polymer chain length does not affect the transferability of the force field and we attribute such transferability mainly to the finer model used in describing the polyamide-6,6 than the polystyrene.

[1]  Florian Müller-Plathe,et al.  Mapping atomistic simulations to mesoscopic models: a systematic coarse-graining procedure for vinyl polymer chains. , 2005, The journal of physical chemistry. B.

[2]  Theodora Spyriouni,et al.  Coarse-Grained and Reverse-Mapped United-Atom Simulations of Long-Chain Atactic Polystyrene Melts: Structure, Thermodynamic Properties, Chain Conformation, and Entanglements , 2007 .

[3]  K. Kremer,et al.  Aggregation and vesiculation of membrane proteins by curvature-mediated interactions , 2007, Nature.

[4]  P. Carreau,et al.  A correlation between critical end-to-end distance for entanglements and molecular chain diameter of polymers , 1991 .

[5]  Gregory A Voth,et al.  Multiscale coarse graining of liquid-state systems. , 2005, The Journal of chemical physics.

[6]  Florian Müller-Plathe,et al.  Coarse-graining in polymer simulation: from the atomistic to the mesoscopic scale and back. , 2002, Chemphyschem : a European journal of chemical physics and physical chemistry.

[7]  K. Schanze,et al.  Hyperbranched conjugated polyelectrolyte bilayers for solar-cell applications. , 2007, Journal of the American Chemical Society.

[8]  F. Müller-Plathe,et al.  Viscosity and Structural Alteration of a Coarse-Grained Model of Polystyrene under Steady Shear Flow Studied by Reverse Nonequilibrium Molecular Dynamics , 2007 .

[9]  Roland Faller,et al.  State point dependence of systematically coarse–grained potentials , 2007 .

[10]  J. E. Mark,et al.  Physical properties of polymers handbook , 2007 .

[11]  Jt Johan Padding,et al.  Coarse-grained molecular dynamics simulations of polymer melts in transient and steady shear flow , 2003 .

[12]  Preparing relaxed systems of amorphous polymers by multiscale simulation: Application to cellulose , 2004 .

[13]  A. Mark,et al.  Coarse grained model for semiquantitative lipid simulations , 2004 .

[14]  A. Sokolov,et al.  When Does a Molecule Become a Polymer , 2004 .

[15]  Jun-ichi Takimoto,et al.  A coarse-graining procedure for flexible polymer chains with bonded and nonbonded interactions , 2002 .

[16]  Hendrik Meyer,et al.  Coarse Graining of Short Polythylene Chains for Studying Polymer Crystallization. , 2006, Journal of chemical theory and computation.

[17]  Florian Müller-Plathe,et al.  YASP: A molecular simulation package , 1993 .

[18]  Dirk Reith,et al.  Deriving effective mesoscale potentials from atomistic simulations , 2002, J. Comput. Chem..

[19]  N. Murthy,et al.  Hydrogen bonding, mobility, and structural transitions in aliphatic polyamides , 2006 .

[20]  B. Hsiao,et al.  Interactions between Crystalline and Amorphous Domains in Semicrystalline Polymers: Small-Angle X-ray Scattering Studies of the Brill Transition in Nylon 6,6 , 1999 .

[21]  D. Bedrov,et al.  Structure of Atactic Polystyrene: A Molecular Dynamics Simulation Study , 2000 .

[22]  Hendrik Meyer,et al.  Formation of Chain-Folded Structures in Supercooled Polymer Melts , 2000, cond-mat/0012264.

[23]  Kurt Kremer,et al.  Hierarchical modeling of polystyrene: From atomistic to coarse-grained simulations , 2006 .

[24]  Michael L. Klein,et al.  A coarse grain model for n-alkanes parameterized from surface tension data , 2003 .

[25]  J. E. Mark.  Polymer Data Handbook , 2009 .

[26]  P. Flory,et al.  Equation-of-state parameters for polystyrene , 1971 .