Pressure Transferable Coarse-Grained Potentials for Polymers under Isothermal and Shock Compression

We present a method for systematic coarse-graining of polymers across a broad range of pressures, applicable for extreme shock loading. To address the problem of transferability across different thermodynamic state points, we include a many-body term inspired from the embedded atom method, implemented as a user potential in LAMMPS. Through a combined iterative Boltzmann inversion and least-squares optimization approach, a coarse-grained model is calibrated along an isothermal compression curve, up to 10 GPa. Verification of the model is then established by comparing predicted bulk moduli, shock Hugoniot P-v and us-up curves with atomistic MD calculations for polyethylene. More rigorous thermodynamic analysis of the new coarse-grained model is examined by fitting a Mie-Gruneisen equation of state from both the atomistic and coarse-grained models and examining relationships between compressibility, thermal expansion, and heat capacity. To conclude, potential shortcomings and future work for this new CG model will be discussed.