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Towards a predictive MHD simulation capability for designing hypervelocity magnetically-driven flyer plates and PWclass z-pinch x-ray sources on Z and ZR

Mehlhorn, Thomas A.; Yu, Edmund Y.; Vesey, Roger A.; Cuneo, M.E.; Jones, Brent M.; Knudson, Marcus D.; Sinars, Daniel S.; Robinson, Allen C.; Trucano, Timothy G.; Brunner, Thomas A.; Desjarlais, Michael P.; Garasi, Christopher J.; Haill, Thomas A.; Hanshaw, Heath L.; Lemke, Raymond W.; Oliver, Bryan V.; Peterson, Kyle J.

Abstract not provided.

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TYPE Conference YEAR 2007
OSTI

Beyond the local density approximation : improving density functional theory for high energy density physics applications

Modine, N.A.; Wright, Alan F.; Muller, Richard P.; Sears, Mark P.; Wills, Ann E.; Desjarlais, Michael P.

A finite temperature version of 'exact-exchange' density functional theory (EXX) has been implemented in Sandia's Socorro code. The method uses the optimized effective potential (OEP) formalism and an efficient gradient-based iterative minimization of the energy. The derivation of the gradient is based on the density matrix, simplifying the extension to finite temperatures. A stand-alone all-electron exact-exchange capability has been developed for testing exact exchange and compatible correlation functionals on small systems. Calculations of eigenvalues for the helium atom, beryllium atom, and the hydrogen molecule are reported, showing excellent agreement with highly converged quantumMonte Carlo calculations. Several approaches to the generation of pseudopotentials for use in EXX calculations have been examined and are discussed. The difficult problem of finding a correlation functional compatible with EXX has been studied and some initial findings are reported.

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TYPE SAND Report YEAR 2006
OSTIDOI

Finite-temperature quasiparticle self-consistent GW approximation

Physical Review B - Condensed Matter and Materials Physics

Faleev, Sergey V.; Van Schilfgaarde, Mark; Kotani, Takao; Léonard, François; Desjarlais, Michael P.

We present an ab initio method for electronic structure calculations of materials at finite temperature (FT) based on the all-electron quasiparticle self-consistent GW (QPSCGW) approximation and Keldysh time-loop Green's function approach. We apply the method to Si, Ge, GaAs, InSb, and diamond and show that the band gaps of these materials universally decrease with increasing temperature in contrast with results of the local density approximation (LDA) of density functional theory where the band gaps universally increase. At temperatures of a few eV the difference between quasiparticle energies obtained in FT QPSCGW and FT LDA approaches is significantly reduced. This result suggests that existing simulations of very high-temperature materials based on the FT LDA are more justified than it might appear from the well-known LDA band gap errors at zero temperature. © 2006 The American Physical Society.

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TYPE SAND Report YEAR 2006
ScopusOSTIDOI

Iterative optimized effective potential and exact exchange calculations at finite temperature

Modine, N.A.; Wright, Alan F.; Muller, Richard P.; Sears, Mark P.; Wills, Ann E.; Desjarlais, Michael P.

We report the implementation of an iterative scheme for calculating the Optimized Effective Potential (OEP). Given an energy functional that depends explicitly on the Kohn-Sham wave functions, and therefore, implicitly on the local effective potential appearing in the Kohn-Sham equations, a gradient-based minimization is used to find the potential that minimizes the energy. Previous work has shown how to find the gradient of such an energy with respect to the effective potential in the zero-temperature limit. We discuss a density-matrix-based derivation of the gradient that generalizes the previous results to the finite temperature regime, and we describe important optimizations used in our implementation. We have applied our OEP approach to the Hartree-Fock energy expression to perform Exact Exchange (EXX) calculations. We report our EXX results for common semiconductors and ordered phases of hydrogen at zero and finite electronic temperatures. We also discuss issues involved in the implementation of forces within the OEP/EXX approach.

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TYPE Conference YEAR 2006
OSTI

Exchange-only optimized effective potential calculation of excited state spectra for He and Be atoms

Muller, Richard P.; Desjarlais, Michael P.

The optimized effective potential (OEP) method allows orbital-dependent functionals to be used in density functional theory (DFT), which, in particular, allows exact exchange formulations of the exchange energy to be used in DFT calculations. Because the exact exchange is inherently self-interaction correcting, the resulting OEP calculations have been found to yield superior band-gaps for condensed-phase systems. Here we apply these methods to the isolated atoms He and Be, and compare to high quality experiments and calculations to demonstrate that the orbital energies accurately reproduce the excited state spectrum for these species. These results suggest that coupling the exchange-only OEP calculations with proper (orbital-dependent or other) correlation functions might allow quantitative accuracy from DFT calculations.

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TYPE SAND Report YEAR 2006
OSTIDOI
Results 126–150 of 166
Results 126–150 of 166