Bottom-up coarse-grain modeling of nanoscale shear bands in shocked α-RDX

An important mechanism of detonation initiation in shock compressed energetic molecular crystals is plastic strain localization producing nanoscale shear bands having a pattern that is strikingly similar across a number of crystals of different symmetries. Particle-based coarse-graining emerges as an uncontested approach to model such phenomena, but requires the development of coarse-grain (CG) force fields for molecular crystals. In this paper, we continue our work on the particle-based MSCG/FM (multiscale coarse-graining through force-matching) modeling of hexahydro-1,3,5-trinitro-s-triazine (RDX) [S. Izvekov and B. M. Rice, J. Chem. Phys. 155: 064503 (2021)], where we reported a one-site density-dependent CG force field for the alpha-RDX crystal. Perhaps the most distinct feature of that force field, referred to as the True-Crystal density-dependent (RDX-TC-DD) model, is its ability to predict the structure of alpha-RDX. We present the method to extend existing density-dependent CG force fields to what we term energy-conserving variants, which are conservative force fields with explicitly computable potential energy functions, and apply the method to obtain the RDX-TC-DDE model, an energy-conserving extension of the RDX-TC-DD force field. We then apply the isoenergetic dissipative particle dynamics (DPD-E) method using the RDX-TC-DDE force field to study the response of alpha-RDX to shock compression, demonstrating nucleation of nanoscale shear bands associated with the elastic-plastic transition. The RDX-TC-DDE model and overall workflow open up possibilities to perform high quality simulation studies of shocked molecular energetic materials. [GRAPHICS] .

Automated summary

This study investigates the important mechanism of detonation initiation in shock compressed energetic molecular crystals using particle-based coarse-graining modeling. It presents a density-dependent coarse-grained force field model that can predict the structure of the crystal and applies it to simulate the nucleation of nanoscale shear bands associated with the elastic-plastic transition.