Intermolecular Forces in Army Research DeCarlos E. Taylor UNCLASSIFIED Intermolecular Forces in Army Research DeCarlos E. Taylor August 2, 2012 UNCLASSIFIED

3% EM performance is proportional to crystal density! EM Design Candidate EM PROPERTIES Structure Heat of formation Density Decomposition pathways Mechanical properties Shock response Thermal stability Sensitivity Quantum Mechanics Computer Model EM performance is proportional to crystal density! 3% Detonation Velocity D = a + b * ρ Detonation Pressure P ~ ρ * D2 Rao Surapenani, ARDEC

20 YEARS! Millions of $$$ Low density! Octanitrocubane Idea: Fully nitrate cubane! High energy content High density High Nitrogen Energetic Materials (EMs) Explosive energy derived from nitrogen instead of oxidation of carbon Low signatures from combustion or detonation Major combustion/explosion product is gaseous nitrogen Types of High-Nitrogen EMs All-nitrogen : Expected energy output: 8 x TNT Only product is nitrogen gas Significant challenge: Stabilization at room conditions High-nitrogen without oxidizing groups: High specific impulse (good propelling charge) Insufficient energy release compared to conventional explosives High-nitrogen with strongly oxidizing groups Adequate explosive energy in comparison with conventional explosives Sensitivity issues Performance expectations were not met! SUPER EXPLOSIVE!!! Low density! Approved for public release: distribution unlimited

QM Methods in Army Research Semiempirical NDDO (AM1, PM3, MNDO/d) Perturbation Theory MBPT(2), SAPT Quantum Mechanics Density Functional Theory Coupled Cluster Theory CCSD, CCSD(T), EOM UNCLASSIFIED

Computational Research in EMs Virtual Design New Energetic Materials Energetic Formulations “Computational Toolkit” Disruptive Energetics ·QM characterization of non-conventional energetics ·Release of stored energy in ND ·Dynamic response of shocked poly-N Multiscale Response of Energetic Materials Development of meso-scale models of heterogeneous EM Development of models relating hot spot dynamics to microstructure Bottom-up meso-particle dynamics models Virtual testing of EM in munitions Note that Disruptives deliverables could be supported under this RA or under the Disruptives Energetics RA Approved for public release: distribution unlimited

Computational toolbox Ionic materials rms: 4.0% Neutral materials rms: 3.6% Crystal Densities Neutral molecules refit to improve the RMS error to 2.9%! Using quantum mechanics, we have derived correlations to solid phase heats of formation and crystalline densities for both neutral and ionic energetic materials Correlations require calculations only on single molecule (not bulk material) e rich e poor Mapping out e- Density Electrostatic Potential CL20 + Heats of Formation Neutral materials rms < 6 kcal/mol Ionic materials rms error (kcal/mol) Comments 25.0 Requires knowledge of crystal structure 24.0 Requires QM information of single molecule! E. F. C. Byrd and B. M. Rice, “Improved Prediction of Heats of Formation of Energetic Materials Using Quantum Mechanical Calculations”, Journal of Physical Chemistry A (2006) 110, 1005-1013; ibid (2009) 113, 5813. B. M. Rice and E. F. C. Byrd, “Accurate predictions of crystal densities using quantum mechanical molecular volumes”, Journal of Physical Chemistry A (2007) 111(42), 10874-1087 Approved for public release. Distribution is unlimited. Presented under the auspices of DEA 1060

Non-expert User Toolkit Computational Toolbox David Chavez (LANL) Phil Leonard (LANL) Phil Pagoria (LLNL) Damon Parrish (NRL) Jeff Deschamps (NRL) Ripu Malholtra (SRI) David Tevaul (ECBC) Tom Klapotke (LMU) Al Stern (NSWC) Matt Sherrill (ARL) Reddy Damavarapu (ARDEC) Michael Miller (ARDEC) BNDD r(g/cc) = 1.914 (1.870) DHs (kcal/mol) = 145.1 (142) 3,6-Bis(4-nitro-1,2,5-oxadiazol-3-yl)-1,4,2,5-dioxadiazene (BNDD): A Powerful Sensitive Explosive. Leonard, Philip W. Pollard, Colin J; Chavez, David E.; Rice, Betsy M. Parrish, Damon A. SYNLETT 14 ,2097 (2011).  Matt is our control. If it works for Matt, it will work for anyone “Have I told you lately how much I LOVE the new script! It makes everything so much easier! Thanks! You are the best!” 12/12/2011 Non-expert User Toolkit (Designed by Ed Byrd) Simple Input (xyz) Submit one job, answers pop out. Write paper and wow your friends with your theoretical acumen. We have a special DSRC account for you to use (“The Sandbox”)!

15 GPa Disruptive Energetics Polymeric CO Polymeric Nitrogen Nanodiamonds Surface reconstruction New polymeric crystalline phase! 15 GPa High Velocity Collisions

Temperature and stress is important (MD) UNCLASSIFIED Hexanitrobenzene Fox-7 DATB Trinitrobenzene Trinitrotoluene Energetic Molecular Crystals TATB Trinitroaniline Large unit cells Condensed phase (periodicity) Temperature and stress is important (MD)

DFT – Energetic Molecular Crystals 3% Maximum Allowable Error UNCLASSIFIED

Dispersion - TATB UNCLASSIFIED SAPT Interaction Energy Electrostatic=0.44 Induction=-2.68 Dispersion=-8.52 Total=-3.60 SAPT Interaction Energy Electrostatic=-4.89 Induction=-5.301 Dispersion=-16.47 Total=-10.05 SAPT Interaction Energy Electrostatic=-4.63 Induction=-3.08 Dispersion=-7.57 Total=-5.93 SAPT Interaction Energy Electrostatic=-5.43 Induction=-7.87 Dispersion=-22.47 Total=-11.65 Symmetry Adapted Perturbation Theory Fit intermolecular potential (exp-6) 900 ab initio data points Minima on fitted surface analyzed with ab initio SAPT(DFT) SAPT Interaction Energy Electrostatic=-4.07 Induction=-1.84 Dispersion=-4.06 Total=-4.47 SAPT Interaction Energy Electrostatic=-3.87 Induction=-2.16 Dispersion=-5.12 Total=-4.80 SAPT Interaction Energy Electrostatic=-4.47 Induction=3.71 Dispersion=-9.22 Total=-6.09 UNCLASSIFIED

Fox-7 Maximum Error Edge lengths: 0.83% Cell angles: 0.24% SAPT Potential Experiment Maximum Error Edge lengths: 0.83% Cell angles: 0.24% Density: 0.37% UNCLASSIFIED

Dispersion Corrections SOFTWARE CP2K VASP Dispersion Corrected Atom-centered Potentials (DCACPS) DFT-D* (Grimme) CCSD(T) Fitted to CCSD(T) interaction energies UNCLASSIFIED

DCACPS – Energetic Molecular Crystals RDX HMX PETN TATB UNCLASSIFIED

Ambient pressure ionic high nitrogen EMs % error in density UNCLASSIFIED

DFT-D Energetic Molecular Crystals TATB HMX PETN UNCLASSIFIED

“What is the state of the art?” Motivation Quantum Mechanics Is Foundation Of Our Program! “What is the state of the art?” Atomistic Subgrain Single crystal Polycrystal Continuum The number of different approaches New density functionals Virtual orbital approaches Pseudopotential methods Empirical Corrections Different benchmark systems

Coupled Cluster Benchmarks Imidazole Water Methyl Formate Benzene-Methane Benzene-Water Ethanol Nitromethane Nitrobenzene EDNA Fox-7 2 Million CPU Hours

What is “best” option for advancing the needs of the Army? Discussion What is “best” option for advancing the needs of the Army? Density Functionals vs. Empirical Corrections C6R-6 corrections do not change electronic structure “…all non-empirical attempts to introduce van der Waals interaction in DFT will finally end up with methods that will be at least at compex as the simplest wavefunction methods.” Perspectives on application to large systems