We introduce a new method for optimizing minimal energy conical intersections (MECIs), based on sequential penalty constrained optimization in conjunction with smoothing function. The is applied to optimize MECI geometries using the multistate formulation of second-order multireference perturbation theory (MS-CASPT2). Resulting and energetics conjugated molecules including ethylene, butadiene, stilbene, green fluorescent protein chromophore are compared state-averaged complete active space...

We demonstrate the existence of a simultaneous degeneracy (not required by symmetry) three electronic states in malonaldehyde. This is one first reports such triple involving S0, S1, and S2 molecule with closed-shell ground state. further report on two-state S2/S1 conical intersection which higher energy than three-state intersection, but closer to Franck−Condon point. First-principles quantum dynamics calculations photochemistry after excitation show that there competition between these...

We present the first calculations of excited-state dynamics using ab initio molecular with a multireference perturbation theory description electronic structure. The new AIMS-CASPT2 method is applied to paradigmatic intramolecular proton-transfer reaction in methyl salicylate, and results are compared previous ultrafast spectroscopic experiments. Agreement experimental quantitative. demonstrate that lack an observed isotope effect due multidimensionality coordinate, which largely involves...

Excited-state potential energy surface (PES) characterization is carried out at the CASSCF and MRSDCI levels, followed by ab initio dynamics simulation of excited-state intramolecular proton transfer (ESIPT) on S2(ππ*) state in malonaldehyde. The proton-transfer transition lies close to an S2/S1 conical intersection, leading substantial coupling with electronic relaxation. Proton exchange proceeds freely S2, but its duration limited competition twisting molecular plane. This rotamerization...

The full multiple spawning (FMS) method has been developed to simulate quantum dynamics in the multistate electronic problem. In FMS, nuclear wave function is represented a basis of coupled, frozen Gaussians, and "spawning" procedure prescribes means adaptively increasing size this order capture population transfer between states. Herein we detail new algorithm for specifying initial conditions newly spawned functions that minimizes number needed convergence. "Optimally" are placed maximize...

Femtosecond time-resolved photoelectron spectroscopy and high-level theoretical calculations were used to study the effects of methyl substitution on electronic dynamics alpha,beta-enones acrolein (2-propenal), crotonaldehyde (2-butenal), methylvinylketone (3-buten-2-one), methacrolein (2-methyl-2-propenal) following excitation S2(pipi*) state at 209 200 nm. We determine that molecules move rapidly away from Franck-Condon region, reaching a conical intersection promoting relaxation S1(npi*)...

Polymers and foams are pervasive in everyday life, as well specialized contexts such space exploration, industry, defense. They frequently subject to shock loading the latter cases, will chemically decompose small molecule gases carbon (soot) under loads of sufficient strength. We review a body work—most it performed at Los Alamos National Laboratory—on polymers extreme conditions. To provide some context, we begin with brief basic concepts shockwave physics, including features particular...

A calibration of the AWSD (Arrhenius Wescott-Stewart-Davis) reactive flow model, applied to HMX based explosive PBX 9501 is presented. Requisite equation state parameters for high reactants and products are on a combination experimental data theoretical calculations. The needed calibrate reaction rate specifically shock detonation transition propagation at variety initial temperatures, presented along with model results planned future activities.

We discuss the connectivity of intersection spaces and role minimal energy points within these (minimal conical intersections or MECIs) in promoting nonadiabatic transitions. focus on malonaldeyde as a specific example, where there is low-lying three-state intersection. This global minimum bright excited electronic state, but it plays limited population transfer our ab initio multiple spawning (AIMS) simulations because molecule must traverse series two-state to reach Due differences seam...

The structural phase stability of 1,1-diamino-2,2-dinitroethylene (FOX-7) has been studied up to 10 GPa through isothermal compression at 100 °C and 200 using synchrotron mid- far-infrared spectroscopy. During changes are observed in vibrational spectra with increase pressure that indicative significant distortion monoclinic α or a possible transformation high α′ 2.2 α″ 6.1 GPa. At °C, for the far- mid-IR regimes, similar were 2.1 (2.0) 5.3 (5.5) GPa, respectively. change is nearly isobaric,...

Shock compression of two molded, carbon fiber-filled polymer composites was performed in gas gun-driven plate impact experiments at velocities up to ≈5 km/s. Hugoniot states for both were obtained from <5 GPa nearly 50 GPa. The materials contained a high fill percentage chopped fibers, bound by either phenolic or cyanate ester polymeric resins. Their dynamic responses similar, although the 10 wt. % difference produced measureable divergence shock compressibility. fibers matrix led...

The room temperature stability of 3,3'-diamino-4,4'-azoxyfurazan (DAAF) has been investigated using synchrotron far-infrared, mid-infrared, Raman spectroscopy, and X-ray diffraction (XRD) up to 20 GPa. as-loaded DAAF samples exhibited subtle pressure-induced ordering phenomena (associated with positional disorder the azoxy "O" atom) resulting in doubling a-axis, form a superlattice similar low-temperature polymorph. Neither high pressure XRD, nor infrared or spectroscopies indicated presence...

Excited state intramolecular proton transfer (ESIPT) and electronic relaxation in o-hydroxybenzaldehyde (OHBA) are simulated using ab initio multiple spawning (AIMS) dynamics, the results compared with those obtained for closely related molecules malonaldehyde methyl salicylate. The role of ordering (more specifically, placement spectroscopically dark states) is examined context tautomerisation yield. When a nπ* character lies between optically accessible S0, extent ESIPT hindered.

We present the results of plate impact experiments performed on 30%–75% porous, polymeric methylene diphenyl diisocyanate polyurethane foams. The combination new data with those previously obtained full-density material was used to calibrate complete equations-of-state under both inert and chemically reactive frameworks. Description unreacted based a Hayes P-α models, whereas its decomposition products were predicted via free energy minimization assumption chemical thermodynamic equilibrium....

The low- and high-strain-rate compaction response of three distinct morphology CeO2 powders was measured experimentally. At low-strain-rates, the compression path found to vary with initial particle as a result differences in packing structure rearrangement at low stresses. However, similar responses were observed higher stresses under low-strain-rate loading. Dynamic experiments performed impact velocities between 0.15 0.78 km/s, resulted 0.51-4.59 GPa powders. In contrast behavior dynamic...

2,4,6-trinitrotoluene (TNT) is a molecular explosive that exhibits chemical stability in the molten phase at ambient pressure. A combination of visual, spectroscopic, and structural (x-ray diffraction) methods coupled to high pressure, resistively heated diamond anvil cells was used determine melt decomposition boundaries >15 GPa. The TNT found be limited, existing small domain pressure-temperature conditions below 2 Decomposition dominates diagram temperatures beyond 6 From...

An optimized variant of the nested Markov chain Monte Carlo [n(MC)(2)] method [J. Chem. Phys. 130, 164104 (2009)] is applied to fluid N(2). In this implementation n(MC)(2), isothermal-isobaric (NPT) ensemble sampling on basis a pair potential (the "reference" system) used enhance efficiency based Perdew-Burke-Ernzerhof density functional theory with 6-31G(*) set (PBE6-31G(*), "full" system). A long sequence steps taken in reference system converted into trial step full system; for good...

We present the first application of reactive Monte Carlo in a first-principles context. The algorithm samples modified NVT ensemble which volume, temperature, and total number atoms given type are held fixed, but molecular composition is allowed to evolve through stochastic variation chemical connectivity. discuss general features method, as well techniques needed enhance efficiency Boltzmann sampling. Finally, we compare results simulation NH3 those ab initio dynamics (AIMD). find that...

The equation of state (EOS) carbon is important in high explosive, geophysical, and inertial confinement fusion applications. Within the semi-empirical Sesame framework, EOS each phase represented by a sum cold, vibrational, thermal electronic Helmholtz free energy contributions. Each has ∼5-10 independent parameters that are adjusted to reproduce single-phase data (e.g., expansion, isothermal compression) as well experimentally- computationally- derived boundaries. Manual calibration full...

Polysulfone was shock loaded to pressures of 14.6–26.2 GPa in a series gas gun-driven plate-impact experiments measuring material response with embedded electro-magnetic particle velocity gauges and optical velocimetry. The did not show distinct two-wave structure but rounding that suggested reaction separation the reactants product waves. In contrast, transmission fielded velocimetry, ranging from 21.0 26.2 GPa, showed well-defined structures due shock-driven chemical decomposition polymer...

We performed a series of six plate impact experiments on polyimide and modeled them using new reactant products equations state combined with an Arrhenius rate model. The first experiment was diagnosed embedded electromagnetic velocity gauges through which we directly observed attenuation the lead shock to approximately constant over propagation distance roughly 4 mm. Simulated gauge profiles were in excellent qualitative agreement suggested sluggish chemical reaction that did not proceed...

We construct new equations of state (EOS) for high density and ultrahigh molecular weight polyethylene their chemical decomposition products under shock loading. The former were built using the SESAME framework, based in part on specific heat thermal expansion data reported here. EOS was thermochemical modeling assumption full thermodynamic equilibrium. are represented as ideal mixture bulk carbon form diamond, H2, H, CH4. In process building a products, we recalibrated our exponential-6...

Polyethylene (C2H4)n was compressed to pressures between 10 and 30 GPa in a diamond anvil cell (DAC) laser heated above 2500 K for approximately one second. This resulted the chemical decomposition of polymer into carbon hydrocarbon reaction products. After quenching ambient temperature, products were measured DAC at ranging from 29 using combination x-ray diffraction (XRD) small angle scattering (SAXS). XRD identified cubic methane as predominant product species with their pressure-volume...