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Stopping of Deuterium in Warm Dense Deuterium from Ehrenfest Time-Dependent Density Functional Theory

Contributions to Plasma Physics

Magyar, Rudolph J.; Shulenburger, Luke N.; Baczewski, Andrew D.

In these proceedings, we show that time-dependent density functional theory is capable of stopping calculations at the extreme conditions of temperature and pressure seen in warm dense matter. The accuracy of the stopping curves tends to be up to about 20% lower than empirical models that are in use. However, TDDFT calculations are free from fitting parameters and assumptions about the model form of the dielectric function. This work allows the simulation of ion stopping in many materials that are difficult to study experimentally. (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim).

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TYPE Conference Poster YEAR 2016
ScopusOSTIDOI

Ethane-xenon mixtures under shock conditions

Physical Review B - Condensed Matter and Materials Physics

Magyar, Rudolph J.; Root, Seth R.; Cochrane, Kyle C.; Mattsson, Thomas M.; Flicker, Dawn G.

Mixtures of light elements with heavy elements are important in inertial confinement fusion. We explore the physics of molecular scale mixing through a validation study of equation of state (EOS) properties. Density functional theory molecular dynamics (DFT-MD) at elevated temperature and pressure is used to obtain the thermodynamic state properties of pure xenon, ethane, and various compressed mixture compositions along their principal Hugoniots. To validate these simulations, we have performed shock compression experiments using the Sandia Z-Machine. A bond tracking analysis correlates the sharp rise in the Hugoniot curve with the completion of dissociation in ethane. The DFT-based simulation results compare well with the experimental data along the principal Hugoniots and are used to provide insight into the dissociation and temperature along the Hugoniots as a function of mixture composition. Interestingly, we find that the compression ratio for complete dissociation is similar for several compositions suggesting a limiting compression for C-C bonded systems.

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TYPE Journal Article YEAR 2015
ScopusOSTIDOI

Validating density-functional theory simulations at high energy-density conditions with liquid krypton shock experiments to 850 GPa on Sandia's Z machine

Physical Review B - Condensed Matter and Materials Physics

Mattsson, Thomas M.; Root, Seth R.; Mattsson, Ann E.; Shulenburger, Luke N.; Magyar, Rudolph J.; Flicker, Dawn G.

We use Sandia's Z machine and magnetically accelerated flyer plates to shock compress liquid krypton to 850 GPa and compare with results from density-functional theory (DFT) based simulations using the AM05 functional. We also employ quantum Monte Carlo calculations to motivate the choice of AM05. We conclude that the DFT results are sensitive to the quality of the pseudopotential in terms of scattering properties at high energy/temperature. A new Kr projector augmented wave potential was constructed with improved scattering properties which resulted in excellent agreement with the experimental results to 850 GPa and temperatures above 10 eV (110 kK). Finally, we present comparisons of our data from the Z experiments and DFT calculations to current equation of state models of krypton to determine the best model for high energy-density applications.

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TYPE Journal Article YEAR 2014
ScopusOSTIDOI

Numerical implementation of time-dependent density functional theory for extended systems in extreme environments

Baczewski, Andrew D.; Shulenburger, Luke N.; Desjarlais, Michael P.; Magyar, Rudolph J.

In recent years, DFT-MD has been shown to be a useful computational tool for exploring the properties of WDM. These calculations achieve excellent agreement with shock compression experiments, which probe the thermodynamic parameters of the Hugoniot state. New X-ray Thomson Scattering diagnostics promise to deliver independent measurements of electronic density and temperature, as well as structural information in shocked systems. However, they require the development of new levels of theory for computing the associated observables within a DFT framework. The experimentally observable x-ray scattering cross section is related to the electronic density-density response function, which is obtainable using TDDFT - a formally exact extension of conventional DFT that describes electron dynamics and excited states. In order to develop a capability for modeling XRTS data and, more generally, to establish a predictive capability for rst principles simulations of matter in extreme conditions, real-time TDDFT with Ehrenfest dynamics has been implemented in an existing PAW code for DFT-MD calculations. The purpose of this report is to record implementation details and benchmarks as the project advances from software development to delivering novel scienti c results. Results range from tests that establish the accuracy, e ciency, and scalability of our implementation, to calculations that are veri ed against accepted results in the literature. Aside from the primary XRTS goal, we identify other more general areas where this new capability will be useful, including stopping power calculations and electron-ion equilibration.

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TYPE SAND Report YEAR 2014
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LDRD project 151362 : low energy electron-photon transport

Kensek, Ronald P.; Hjalmarson, Harold P.; Magyar, Rudolph J.; Bondi, Robert J.

At sufficiently high energies, the wavelengths of electrons and photons are short enough to only interact with one atom at time, leading to the popular %E2%80%9Cindependent-atom approximation%E2%80%9D. We attempted to incorporate atomic structure in the generation of cross sections (which embody the modeled physics) to improve transport at lower energies. We document our successes and failures. This was a three-year LDRD project. The core team consisted of a radiation-transport expert, a solid-state physicist, and two DFT experts.

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TYPE SAND Report YEAR 2013
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Results 1–25 of 54
Results 1–25 of 54