Bulletin of the American Physical Society
19th Biennial Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 60, Number 8
Sunday–Friday, June 14–19, 2015; Tampa, Florida
Session Z5: First-Principles and MD IX: Energy Relaxation |
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Chair: Alejandro Strachan, Purdue University, Avinash Dongare, University of Connecticut Room: Grand I/J |
Friday, June 19, 2015 11:15AM - 11:30AM |
Z5.00001: A molecular dynamics study of the relaxation of an excited benzene molecule chemisorbed to the surface of crystalline RDX Andrey Pereverzev, Thomas D. Sewell, Andrei Piryatinski Molecular dynamics simulations with a full-dimensional non-reactive potential-energy surface were used to study energy transfer from an excited benzene molecule covalently bonded to the surface of RDX crystal at 298 K and atmospheric pressure. The crystal is treated as a periodic, freestanding thin film approximately 5 nm thick. Initial conditions for the excited molecule were obtained from quantum mechanical calculations. Dominant energy redistribution pathways both in the space of atomic coordinates and in the space of crystal normal modes will be reported. Theoretical models of energy relaxation processes in this and similar systems will be discussed. [Preview Abstract] |
Friday, June 19, 2015 11:30AM - 11:45AM |
Z5.00002: Achieving tunable sensitivity in composite high-energy density materials Sergey Rashkeev, Roman Tsyshevsky, Maija Kuklja Laser irradiation provides a unique opportunity for selective, predictive, and controlled initiation of energetic materials. We propose a consistent micro-scale mechanism of photoexcitation at the interface, formed by a molecular energetic material and a metal oxide. A specific PETN-MgO model composite is used to illustrate and explain seemingly puzzling experiments on selective laser initiation of energetic materials, which reported that the presence of metal oxide additives triggered the photoinitiation by an unusually low energy. We suggest that PETN photodecomposition is catalyzed by oxygen vacancies (F$^{\mathrm{0}}$ centers) at the MgO surface. The proposed model suggests ways to tune sensitivity of energetic molecular materials to photoinitiation. Our quantum-chemical calculations suggest that the structural defects (e.g., oxygen vacancies) strongly interact with the molecular material (e.g., adsorbed energetic molecules) by inducing a charge transfer at the interface and hence play an imperative role in governing both energy absorption and energy release in the system. Our approach and conclusions provide a solid basis for novel design of energetic interfaces with desired properties and offers a new perspective in the field of explosive materials and devices. [Preview Abstract] |
Friday, June 19, 2015 11:45AM - 12:00PM |
Z5.00003: Molecular dynamic study of Shock wave response of bulk amorphous polyvinyl chloride: effect of chain length and force field Anupam Neogi, Nilanjan Mitra Atomistic molecular dynamics in conjunction with multi-scale shock technique is utilized to investigate shock wave response of bulk amorphous polyvinyl chloride. Dependence of chain length on physical and mechanical behaviour of polymeric material at ambient condition of temperature and pressure are well known but unknown for extreme conditions. Non-reactive force fields PCFF, COMPASS and PCFF+ were used to determine applicability of the force field for the study of the material subjected to shock loads. Several samples of PVC with various chain lengths were subjected to a range of shock compression from 1.5-10.0 km/s. Even though dependence of chain length was observed for lower shock strengths but was not for intense shock loads. The principle Hugoniot points, calculated by applying hydrostatic Rankine-Hugoniot equations and as well as multi-scale shock technique, were compared against LASL experimental shock data, demonstrating superior performance of PCFF+ force-field over PCFF and COMPASS. Shock induced melting characteristic and vibrational spectroscopic study were conducted and compared with experimental data to observe differences in response with relation to different force fields, chain length of the material for different shock intensities. [Preview Abstract] |
Friday, June 19, 2015 12:00PM - 12:15PM |
Z5.00004: The hydriding resistance of plutonium oxides and mononitride: A view from $ab$ $initio$ molecular dynamics Bo Sun, Haifeng Liu, Haifeng Song Based on the non-local van der Waals density functional (vdW-DF)+$U$ scheme, we carry out the $ab$ $initio$ molecular dynamics study of the interaction dynamics for H2 molecules impingement against Pu-oxides and mononitride surfaces. We show that except for the weak physisorption, both PuO2 and PuN surfaces are so difficult of access that almost all of H2 molecules will bounce back to the vacuum when their initial kinetic energies are not sufficient. Although the dissociative adsorption of H2 on PuO2 surfaces is found to be exothermic, the collision-induced dissociation barriers of H2 are very high (up to 2.2 eV). However, PuO2 overlayer on Pu-metal can be reduced to $\alpha$-Pu2O3 drived by oxygen-lean conditions, and H2 can penetrate and diffuse in $\alpha$-Pu2O3 easily. As a result, $\alpha$-Pu2O3 can promote the hydriding process of Pu. Unlike PuO2, PuN is found to be one kind of stable and uniform passivation layer against Pu-hydriding. Specifically, the incorporation of PuN and H-atom is proven to be thermodynamically unstable. Overall, our current study reveals the mechanical and chemical resistances of Pu-oxide and Pu-nitride to hydrogen corrosion, which have strong implications to the understanding of the surface corrosion and passivation of Pu metal. [Preview Abstract] |
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