 |
Center for Nonlinear Studies |
Understanding material response and chemistry under extreme conditions is critical for developing informed multi-scale, multi-physics models, but many properties and processes are beyond the current resolution of experiments. Molecular dynamics can predict mechanics, transport, and chemistry in molecular materials, but is often encumbered by competing needs in computational efficiency and physical accuracy required to capture dynamic processes with features on multiple time and length scales. We are developing multiple methods to push the envelope on these constraints and gain insight into fundamental reactivity, anisotropic mechanics during shocks, and to quantify the limitations of continuum transport theory. Recent examples from these three areas will be summarized, highlighting their interconnected nature in predicting the response of materials at extremes and the roles of various modeling techniques in pursuit of this larger goal. Force matching is leveraged to significantly improve the chemical accuracy of efficient density functional tight binding (DFTB) models, which are able to access experimental time scales. The resulting models are employed in ensemble-based investigations to inform statistically justified (and scalable) characterizations of CNHO chemistry and phase transformations under extreme conditions. A generalized crystal-cutting method (GCCM) is outlined that overcomes many limitations for simulating low-symmetry materials in 3D-periodic cells and gives direct access to orientation-dependent properties. The GCCM is applied to characterize the anisotropic shock response of TATB single crystals and grain boundaries, revealing new deformation mechanisms and modes for energy localization (e.g., hot spot formation). Applicability of continuum transport models is quantified by scale bridging with molecular dynamics predictions for inherently anisotropic and hierarchical energy transport processes. Implications for modeling the dynamic response of low-symmetry energetic materials at various levels of coarse graining are discussed.
Host: Marc Cawkwell