Assessment of reactive force fields for the failure of hydrocarbon chains: Insights from molecular dynamics and density functional theory

Understanding the mechanical behavior of polymer chains at the molecular level is essential for predicting also their bulk properties, including fracture. Here we investigate the tensile elasticity and failure of single polyethylene (PE) chains using both molecular dynamics (MD) simulations and quantum chemical calculations. Simulations were performed on a long PE chain (C202H406) to assess the differences between four reactive force fields (AIREBO, MEAM, ci-ReaxFF and ReaxFF), while a shorter chain (C16H34) was used for direct comparison of the force fields with density functional theory (DFT). Our results indicate that ReaxFF and ci-ReaxFF closely replicate the DFT predictions and approach the available experimental data for the work of fracture of long hydrocarbon chain. AIREBO consistently overestimates failure forces in both molecular dynamics and energy minimization, while the MEAM predictions depend on the computational method: it underestimates failure forces in molecular dynamics simulations but significantly overestimates them in minimization calculations. These findings suggest that ReaxFF and ci-ReaxFF are reliable choices for simulating the scission of polymer chains, and may be used as starting point for more extensive simulations of polymer mechanics and fracture.