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 V5: First-Principles and MD VII: New Materials |
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Chair: Iskander Batyrev, Army Research Laboratory, Maija Kukla, National Science Foundation Room: Grand I/J |
Thursday, June 18, 2015 3:45PM - 4:00PM |
V5.00001: First principle investigation of iron pentacarbonyl energetic solid at high pressure Kien Nguyen Cong, Brad Steele, Aaron Landerville, Ivan Oleynik Polymeric phase of carbon mono-oxide (p-CO), an extended non-molecular solid, is extremely energetic, and therefore represents a new class of low-Z energetic materials. Recently, iron penta-carbonyl Fe(CO)$_{5}$ has been experimentally investigated as a p-CO precursor: the presence of transition metal ions is believed to stabilize p-CO at ambient conditions. Since p-CO forms at high pressures, it becomes important to investigate the high-pressure behavior of Fe(CO)$_{5}$ as well. In this work, first-principles evolutionary structure search method is used to predict the crystal phases of Fe(CO)$_{5}$ at high pressure. Known experimental structure of phase I is confirmed. Moreover, previously unknown structure of phase II is predicted. The Raman spectra, calculated as a function of pressure, were used to demonstrate that the phase III, predicted by a recent experiment, is identical to phase II. [Preview Abstract] |
Thursday, June 18, 2015 4:00PM - 4:15PM |
V5.00002: Modeling of the pressure induced formation of a random network of a mixture of N2 and CO crystals I.G. Batyrev First principles calculations were performed to understand the pressure induced transition to an extended solid of substitutional mixtures of N2 and CO in the crystalline delta phase. The transition occurs at $\sim$ 7-9 GPa and has a hysteresis allowing for the stabilization of a covalently bonded random network to much lower pressures. Only two N atoms out of 24 were found to be incorporated into the random network formed mainly by C and O atoms in a 128 atom unit cell.\footnote{I.G. Batyrev and W.D. Mattson, Journal of Physics: Conference Series 500 (2014) 022006.} Here, in searching for a new route for the synthesis of polynitrogen materials, higher concentrations of N atoms (50{\%}, 90.625, {\%} and 93.75{\%}) in delta molecular crystal phases under compression up to 50 GPa were calculated using density functional theory. The presence of CO is found to facilitate formation of the random network. In order to understand the importance of the initial molecular crystalline structure, calculations were performed for mixtures of N2 and CO in the delta and epsilon phases and at different sites with spherical and disk-shaped disorder. Calculated IR and Raman spectra are compared with recent experimental results. [Preview Abstract] |
Thursday, June 18, 2015 4:15PM - 4:30PM |
V5.00003: Electride-like phases at extreme compression: towards bridging the gap between theory and experiment Stanimir Bonev The transformation of materials into electride-like structures under the application of extreme pressure has attracted a lot of interest recently. Theoretical studies have predicted the existence of low-coordinated crystal phases, where the conduction electrons are localized in the interstitial atomic regions, for a number of elements at high density. Most of these works have been limited to static lattice calculations. The pressures where such transformations are projected to occur are accessible in shock-wave experiments, but at elevated temperatures. In this talk I will discuss the temperature dependence of elecride structures, both solids and liquids, as well as the requirements for their accurate simulation. [Preview Abstract] |
Thursday, June 18, 2015 4:30PM - 4:45PM |
V5.00004: Nucleation of aluminum nanoclusters on graphene: an ab-initio molecular dynamics study Sufian Alnemrat, Dennis Mayo, Samantha De Carlo, Bryan Eichhorn, Joseph Hooper Recent experimental results have shown that liquid AlCl and AlBr can, in the presence of a reducing agent, nucleate and grow 10-20 nm aluminum nanoparticles on functionalized graphene sheets. This may offer a route to patterned 2D structures of Al nanoparticles and clusters. Here we present DFT and ab initio molecular dynamics simulations of possible nucleation processes on defect-laden graphene beginning with the AlCl precursor. Static calculations show that AlCl weakly physisorbs on perfect graphene, with binding energies less than 0.5 eV and very small barriers for diffusion along the surface. Covalent bonding is seen on graphene only at vacancy sites. Car-Parrinello molecular dynamics is used to study possible cluster nucleation mechanisms near characteristic vacancies. Simulations at 500 and 1000 K show that the AlCl is very reactive in the presence of the defect, quickly agglomerating and forming long AlCl chains with strong Al-Al bonds. [Preview Abstract] |
Thursday, June 18, 2015 4:45PM - 5:00PM |
V5.00005: Simulated Shockwaves in Nanoparticles Embedded Energetics William Mattson, Donald Johnson, Jonathan Mullin Practical energetic materials often consist of mixtures of distinct materials formulated to optimize specific properties. Nanoparticles of traditional as well as novel additives, with their large surface to volume ratio, have been of particular recent interest to the energetics community. Using density functional theory, we have simulated high-velocity shocks of an energetic material containing nanoparticles. We will report on simulations of shocks in crystalline PETN embedded with nanodiamonds of different sizes, and at various shock speeds. [Preview Abstract] |
Thursday, June 18, 2015 5:00PM - 5:15PM |
V5.00006: High-Velocity Collisions of Nanoparticles Donald Johnson, William Mattson Nanoparticles (NPs) are a unique class of material with highly functionalizable surfaces and exciting applications. With a large surface-to-volume ratio and potentially high surface tension, shocked nanoparticles might display unique materials behavior. Using density functional theory, we have simulated high-velocity NP collisions under a variety of conditions. NPs composed of diamond-C, cubic-BN, and diamond-Si were considered with particle sizes up to 3.5 nm diameter. Some simulations involved NPs that were destabilized by incorporating internal strain. Normal, spherical NPs were carved out of bulk crystals and structurally optimized while the NPs with internal strain were constructed as a dense core (compressive strain) encompassed by a thin shell (tensile strain). Both on-axis and off-axis collisions were simulated at various speeds. The amount of internal strain was adjusted by varying the compression ratio of the inner core. Collision dynamics, shock propagation, and fragmentation will be presented and analyzed. The effect of material properties, internal strain, and collision velocity on the final temperature of the fragments will be discussed. [Preview Abstract] |
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