(4cq) Development of a Reactive Semi-Empirical Potential for the Atomistic/Molecular Simulations of Damage and Failure in Polymeric and Polymer/Metal Material System

Molecular dynamics (MD) simulation is a powerful tool for exploring various materials phenomena at the nanoscale. However, successful prediction of these phenomena and associated material properties relies on the availability and use of an interatomic potential that correctly captures the energetics of the atomic interactions. Recently, a great deal of research interest has been expressed towards the MD simulation of damage initiation and evolution in various materials, specifically polymers and polymer/metal systems. Most interatomic potentials do not allow dynamic bond making and bond breaking during simulation, which is a prerequisite for studying the damage phenomena associated with the polymer failure at the molecular scale. Moreover, a great number of potentials have not been parameterized for multicomponent material systems. The objective of this work is to develop an interatomic potential for hydrocarbon-based polymers based on the modified embedded-atom method (MEAM), a reactive semi-empirical N-body potential based on density functional theory and pair potentials. To achieve the objective, an initial parameterization of the MEAM potential was performed for saturated hydrocarbons. The potential was parameterized by fitting to a large experimental and first-principles (FP) database consisting of bond distances, bond angles, and atomization energies of a homologous series of alkanes and their select isomers from methane to n-octane, and various potential energy curves of H₂, CH, and C₂ diatomics, hydrogen, methane, ethane, and propane dimers, and select pressure-volume-temperature (PVT) data of alkanes. The atomization energies and geometries of a range of linear alkanes, cycloalkanes, and free radicals calculated from the MEAM potential were compared to those calculated by other commonly used potentials for hydrocarbons, i.e., second-generation reactive empirical bond order (REBO) and reactive force field (ReaxFF). MEAM reproduced the experimental and/or FP data with great accuracy, comparable to or better than REBO or ReaxFF. The experimental PVT data for a relatively large series of methane, ethane, propane, and butane systems with different densities were predicted reasonably well by MEAM. This work is the first attempt to expand the parameter database of the MEAM potential beyond atomistic systems, i.e., metals and metallic alloys, to covalently bound molecular systems. The details of potential parameterization and results of various atomistic calculations are presented.