A5027196533- Energetic Materials and Combustion
- High-pressure geophysics and materials
- Crystallography and molecular interactions
- Boron and Carbon Nanomaterials Research
- Thermal and Kinetic Analysis
- Diamond and Carbon-based Materials Research
- Chemical Thermodynamics and Molecular Structure
- Combustion and Detonation Processes
- Inorganic Chemistry and Materials
- Chalcogenide Semiconductor Thin Films
- Rocket and propulsion systems research
- High-Velocity Impact and Material Behavior
- 2D Materials and Applications
- Quantum Dots Synthesis And Properties
- Phase Equilibria and Thermodynamics
- Enzyme Structure and Function
- Solid-state spectroscopy and crystallography
- Molecular Spectroscopy and Structure
- Protein Structure and Dynamics
- Luminescence and Fluorescent Materials
- MXene and MAX Phase Materials
- Carbon Nanotubes in Composites
- Advanced Chemical Physics Studies
- Chemical Reactions and Mechanisms
- Nonlinear Optical Materials Research
Lawrence Livermore National Laboratory
2019-2025
Lawrence Livermore National Security
2019-2025
University of South Florida
2013-2019
Argonne National Laboratory
2019
University of Chicago
2019
University of Nevada, Las Vegas
2019
DEVCOM Army Research Laboratory
2017
The pentazolates, the last all-nitrogen members of azole series, have been notoriously elusive for hundred years despite enormous efforts to make these compounds in either gas or condensed phases. Here, we report a successful synthesis solid state compound consisting isolated pentazolate anions N5–, which is achieved by compressing and laser heating cesium azide (CsN3) mixed with N2 cryogenic liquid diamond anvil cell. experiment was guided theory, predicted transformation mixture at high...
Polynitrogen compounds have attracted great interest due to their potential applications as high energy density materials. Most recently, a rich variety of alkali polynitrogens (R_{x}N_{y}; R=Li, Na, and Cs) been predicted be stable at pressures one them, CsN_{5} has recently synthesized. In this work, various potassium polynitrides are investigated using first-principles crystal structure search methods. Several novel molecular crystals consisting N_{4} chains, N_{5} rings, N_{6} rings...
Two new crystalline compounds, pentazole (N_{5}H) and ammonium pentazolate (NH_{4})(N_{5}), both featuring cyclo-{\rm N_{5}^{-}} are discovered using first principles evolutionary search of the nitrogen-rich portion hydro-nitrogen binary phase diagram (N_{x}H_{y}, x\geqy) at high pressures. Both crystals consist N_{5}^{-} anion NH_{4}^{+} or hydrogen H^{+} cations. These two predicted to be thermodynamically stable pressures above 30 GPa for (NH_{4})(N_{5}) 50 N_{5}H. The chemical...
First-principles crystal structure search is performed to predict novel rubidium poly-nitrogen materials at high pressure by varying the stoichiometry, i.e., relative quantities of constituent and nitrogen atoms. Three compounds content, RbN5, RbN2, Rb4N6, are discovered. Rubidium pentazolate (RbN5) becomes thermodynamically stable pressures above 30 GPa. The charge transfer from Rb N atoms enables aromaticity in cyclo-N5- while increasing ionic bonding crystal. can be synthesized...
Machine-learned interatomic models have growing in popularity due to their ability afford near quantum-accurate predictions for complex phenomena, with orders-of-magnitude greater computational efficiency. However, these struggle when applied systems of many element types the exponential increase number parameters that must be determined. To mitigate this challenge, we present a new hierarchical transfer learning approach allows fitting problem decomposed into smaller independent and...
Shock-induced detonation of insensitive high explosives based on 1,3,5-triamino-2,4,6-trinitrobenzene starts with formation hot spots at microstructural defects but has eluded atomistic modeling treatment micron length scales. To this end, we performed multimicron scale all-atom molecular dynamics (MD) simulations that form during the collapse cylindrical pores diameters between 10 and 300 nm. Our MD show formed larger than 20 nm exhibit temperature fields scale-invariant features for sizes...
Determining the unreacted equation of state 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) is challenging because it exhibits low crystal symmetry and X-ray scattering strength. Here, we present first high-pressure single-crystal diffraction (SXD) study this material. Our SXD results reveal a previously unknown transition to monoclinic phase above 4 GPa. No abrupt change volume occurs but compressibility changes. Concomitant principles evolutionary structure prediction USPEX calculations...
2,6-Diamino-3,5-dinitropyrazine-1-oxide (LLM-105) is a relatively new and promising insensitive high-explosive (IHE) material that remains only partially characterized. IHEs are of interest for range applications from fundamental science standpoint, as the root causes behind insensitivity poorly understood. We adopt multitheory approach based on reactive molecular dynamic simulations performed with density functional theory, tight-binding, force fields to characterize reaction pathways,...
Compressive shearing forces can induce mechanochemical oligomerization reactions in glycine.
2,4,6-triamino-1,3,5-trinitrobenzene (TATB) is an insensitive High Explosive (HE) that widely studied to better understand the physical properties of safety and sensitivity HE. A dominant initial decomposition mechanism TATB believed be a dehydration reaction forms mono- di-furazans, although other mechanisms have been reported. In this work, seven were modeled with ab initio simulations calculate its free energy barriers, rates, kinetic isotope effects. The barrier for mono-benzofurazan was...
Amorphous carbon (a-C) has attracted considerable interest due to its desirable properties, which are strongly dependent on structure, density and impurities. Using ab initio molecular dynamics simulations we show that the sp2/sp3 content underlying structural order of a-C produced via liquid quenching evolve at high temperatures pressures sub-nanosecond timescales. Graphite-like densities ([Formula: see text] 2.7 g/cc) favor formation layered arrangements characterized by sp2 disordered...
Ternary CxNyOz compounds are actively researched as novel high energy density and ultrahard materials. Although some synthesis work has been performed at ambient conditions, very little is known about the pressure chemistry of compounds. In this work, first-principles variable-composition evolutionary structure prediction calculations with goal discovering mixed materials conditions. By systematically searching ternary variable composition crystalline materials, full phase diagram...
The high-pressure equation of state (EOS) energetic materials (EMs) is important for continuum and mesoscale models detonation performance initiation safety. Obtaining a high-fidelity EOS the insensitive EM 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) has proven to be difficult because challenges in experimental characterization at high pressures (HPs). In this work, powder X-ray diffraction patterns were fitted using recently discovered monoclinic I2/a phase above 4 GPa, which shows that...
We explore the structural evolution of highly oriented pyrolytic graphite (HOPG) under detonation-induced shock conditions using in situ synchrotron x-ray diffraction ns timescale. observe formation hexagonal diamond (lonsdaleite) at pressures above 50 GPa, qualitative agreement with recent gas gun experiments. First-principles density functional calculations reveal that uniaxial compression, energy barrier for transition toward is lower than cubic diamond. Finally, no indication was...
High explosive detonation starts with formation of hot spots at microstructural defects but has eluded "full physics" atomistic modeling treatment micron length scales. To this end, we develop an image distinguishability analysis to summarize multimicron all-atom MD simulations spot for pore sizes between 10 and 300 nm show that all the smallest exhibit self-similar size scaling. Through grain-scale link behavior material’s rate-insensitive mechanical strength. Our results bolster confidence...
Tin sulfides, Sn x S y , are an important class of materials that actively investigated as novel photovoltaic and water splitting materials. A first-principles evolutionary crystal structure search is performed with the goal constructing complete phase diagram discovering new phases well compounds varying stoichiometry at ambient conditions pressures up to 100 GPa. The SnS2 P3¯m1 symmetry remains stable 28 Another phase, SnS, experiences a series transformations including α-SnS β-SnS 9 GPa,...
This concomitant experimental and theoretical study provides a definitive EOS for α-glycine up to the record pressure of 50 GPa.
Crystal structure prediction (CSP) is performed for the energetic materials (EMs) LLM-105 and α-RDX, as well α β conformational polymorphs of 1,3,5,7-tetranitro-1,3,5,7-tetraazacyclooctane (HMX), using genetic algorithm (GA) code, GAtor, its associated random generator, Genarris. Genarris GAtor successfully generate experimental structures all targets. GAtor's symmetric crossover scheme, where space group symmetries parent are treated genes inherited by offspring, found to be particularly...
Efforts to synthesize, characterize, and recover novel polynitrogen energetic materials have driven attempts subject high nitrogen content precursor (in particular, metal nonmetal azides) elevated pressures. Here we present a combined theoretical experimental study of the high-pressure behavior ammonium azide (NH4N3). Using density functional theory, considered relative thermodynamic stability material with respect two other crystal phases, namely, trans-tetrazene (TTZ), also hydronitrogen...
SnxSey crystalline compounds consisting of Sn and Se atoms varying compositions are systematically investigated at pressures from 0 to 100 GPa using the first-principles evolutionary crystal structure search method based on density functional theory. All known experimental phases SnSe SnSe2 found without any prior input. A second-order polymorphic phase transition SnSe-Pnma SnSe-Cmcm is predicted 2.5 GPa. Initially being semiconducting, this becomes metallic 7.3 Upon further increase...
Abstract High-rate strength behavior plays an important role in the shock initiation of high explosives, with plastic deformation serving to localize heat into hot spots and as a mechanochemical means enhance reactivity. Recent simulations predict that detonation-like shocks produce highly reactive nanoscale shear bands layered crystalline explosive TATB (1,3,5-triamino-2,4,6-trinitrobenzene), but thresholds leading this response are poorly understood. We utilize molecular dynamics simulate...
Abstract Understanding the thermal decomposition behavior of TATB (1,3,5-triamino-2,4,6-trinitrobenzene) is a major focus in energetic materials research because safety issues. Previous and modelling efforts have suggested benzo-monofurazan condensation producing H 2 O initiating step. However, early evolving CO (m/z 44) along with 18) evolution been observed by mass spectrometric monitoring head-space gases both constant heating rate isothermal studies. The source has not explained, until...
We investigated the effects of hydrostatic pressure on α-glycylglycine (α-digly) using a combined experimental and theoretical approach. The results powder X-ray diffraction show change in compressibility axes above 6.7 GPa, but also indicate that structure remains same monoclinic space group, suggesting an isosymmetric phase transition. A noticeable Raman spectra between 6 7.5 GPa further supports observed First-principles-based calculations with crystal prediction code USPEX predict number...