Bulletin of the American Physical Society
20th Biennial Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 62, Number 9
Sunday–Friday, July 9–14, 2017; St. Louis, Missouri
Session L5: First Principles and Molecular Dynamics V |
Hide Abstracts |
Chair: Mark Elert, U. S. Naval Academy Room: Regency Ballroom B |
Tuesday, July 11, 2017 3:45PM - 4:00PM |
L5.00001: Molecular Dynamics Simulations of Rapidly Heated RDX Mark Elert, Ryan Le, Samuel Emery, Paul Giannuzzi, Daniel McCarthy, Igor Schweigert As part of a study of the possible use of explosively generated plasmas to induce deflagration in energetic materials, we have investigated the short-time dynamics of rapidly heated RDX using a version of the ReaxFF reactive potential model optimized for energetic materials simulations. For an RDX crystal heated at one end, we have examined the propagation of energy and reactivity as a function of time. We have also performed MD simulations on a uniformly heated RDX crystal at a range of temperatures up to 8000 K, to investigate the temperature vs. time profile and the detailed kinetics of the deflagration process. [Preview Abstract] |
Tuesday, July 11, 2017 4:00PM - 4:15PM |
L5.00002: Dependence of hotspot criticality on molecular structure: amorphous vs. crystalline RDX Michael Sakano, Brenden Hamilton, Md Mahbubul Islam, Alejandro Strachan Recent large-scale molecular dynamics (MD) simulations showed that hotspots resulting from the dynamical collapse of a void are significantly more reactive that nominally identical ones (in terms of size and thermodynamic conditions) but created under equilibrium conditions. In this work we assess whether the molecular disorder caused by the pore collapse is the main culprit for the increased reactivity of the dynamical hot spot. We use MD with the reactive force field ReaxFF to characterize the kinetics of decomposition of crystalline and amorphous RDX and to characterize the criticality of cylindrical hotspots in both materials. The simulations indicate negligible differences in the reactivity between the two structures when subjected to homogeneous heating. We also studied the chemical decomposition and reaction of cylindrical hotspots of various sizes and temperatures in the two structures. Our preliminary results indicate that hotspots in amorphous RDX are more reactive and, for a given size, transition to a deflagration wave at lower temperatures. We will discuss the possible origin of these surprising observation, including differences in thermal conductivity, temperature-induced structural transformations and the difference in exothermicity between the two systems.. [Preview Abstract] |
Tuesday, July 11, 2017 4:15PM - 4:30PM |
L5.00003: Reaction Analysis of Shocked Nitromethane using Extended Lagrangian Born-Oppenheimer Molecular Dynamics Romain Perriot, Ed Kober, Sue Mniszewski, Enrique Martinez, Anders Niklasson, Ping Yang, Shawn McGrane, Marc Cawkwell Characterizing the complex, rapid reactions of energetic materials under conditions of high temperatures and pressures presents strong experimental and computational challenges. The recently developed extended Lagrangian Born-Oppenheimer molecular dynamics formalism enables the long-term conservation of the total energy in microcanonical trajectories, and using a density functional tight binding formulation provides good chemical accuracy. We use this combined approach to study the evolution of temperature, pressure, and chemical species in shock-compressed liquid nitromethane over hundreds of picoseconds. The chemical species seen in nitromethane under shock compression are compared with those seen under static high temperature conditions. A reduced-order representation of the complex sequence of chemical reactions that characterize this system has been developed from the molecular dynamics simulations by focusing on classes of chemical reactions rather than specific molecular species. Time-resolved infra-red vibrational spectra were also computed from the molecular trajectories and compared to the chemical analysis. These spectra provide a time history of the species present in the system that can be compared directly with recent experiments at LANL. [Preview Abstract] |
Tuesday, July 11, 2017 4:30PM - 4:45PM |
L5.00004: Hydrogen transfer in energetic materials from ReaxFF and DFT calculations Oleg Sergeev, Alexey Yanilkin Reactive molecular dynamics is a tool enabling studies of thermal decomposition of explosives at realistic time scales. In the present work we construct a kinetic model of thermal decomposition of isolated molecules and condensed phase of PETN using results of ReaxFF simulations. The obtained parameters indicate that the activation energy is lowered by 50 kJ/mol in condensed phase compared to the unimolecular decomposition. The governing process in condensed phase decomposition proves out to be the intermolecular hydrogen transfer. The intra- and intermolecular hydrogen transfer is studied in detail with nudged elastic band technique in both ReaxFF and DFT descriptions. Two simpler energetic materials, nitrotoluene and methyl nitrate, are chosen for these calculations to lower the computational cost in DFT. In both materials ReaxFF gives the activation barrier for the intermolecular hydrogen transfer about 100 kJ/mol lower than that in DFT calculations. This may influence the applicability of ReaxFF in kinetics-related simulations of explosives. Computation protocol applied in this work may be used to systematically improve reactive potential for better description of chemical kinetics. [Preview Abstract] |
Tuesday, July 11, 2017 4:45PM - 5:00PM |
L5.00005: Shock wave energy dissipation behavior (SWED) in Network forming ionic liquids (NILs): A Molecular dynamics study Karthik Guda Vishnu, Alejandro Strachan SWED materials play a crucial role in protecting both personnel and structures in close proximity to blasts or ballistic impact. Exposure to shock waves with intensities as low as 1 MPa can cause brain injury in personnel and, hence, it is extremely important to understand the mechanisms operating in SWED materials and help design improved formulations. Recent experimental studies show that NILs containing di-ammonium cations and citrate anions with glass transition temperatures (T$_{\mathrm{g}})$ below room temperature exhibit shockwave absorption characteristics that outperform polyurea (PU), a benchmark SWED assessment material. The experimentalists further hypothesized that the increased SWED ability in NILs with longer side chains (in di-ammonium cation) is due to a permanent structural ordering and nano-scale segregation. We use molecular dynamics simulations with the Dreiding force field to study shock propagation mechanisms in NILs. Shock propagation mechanisms in these materials are explored by performing both Hugoniostat and large scale non-equilibrium molecular dynamics (NEMD) simulations at 300 K. The simulation results show that the NIL 5-6 (5 C atoms (back bone) and 6 C atoms (side chain)) attenuates shocks better than NIL 5-3 (3 C atoms (side chain) and higher Tg) and PMMA in agreement with experimental observation. The simulations show that under shock loading the structures lose long range order; we find no evidence of nano-segregation nor or permanent structural changes. [Preview Abstract] |
Tuesday, July 11, 2017 5:00PM - 5:15PM |
L5.00006: Molecular Dynamics Simulations of the First Reactions in Nitrate Ester-based Explosives Marc Cawkwell, Ed Kober, Thomas Myers, Virginia Manner In order to better understand and manipulate explosive sensitivity, we have prepared and analyzed a series of pentaerythritol tetranitrate-based explosives with systematic changes to the molecular structure. Reactive, extended Lagrangian Born-Oppenheimer molecular dynamics simulations have been performed on this series of molecules in the condensed phase to understand how the reactivity changes with the molecular modifications. The net reactions occurring over the first few hundred picoseconds under conditions of static high temperature and shock compression have been identified by an innovative analysis of coordination geometry changes and reaction types rather than attempting to detail each individual reaction. The evolution of temperature and pressure owing to evolving chemistry in the shock compressed materials were also captured accurately. Changes in exothermicity and the populations of intermediate and product moieties are connected to the systematic changes in stoichiometry. The results of the simulations are compared to preliminary estimates of sensitivity derived from small scale impact tests on materials synthesized recently at LANL.~ [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700