Sandia Labs FY22 Laboratory Directed Research & Development Annual Report

IMPROVING PREDICTIVE CAPABILITY IN REHEDS SIMULATIONS WITH FAST, ACCURATE, AND CONSISTENT NONEQUILIBRIUM MATERIAL PROPERTIES.

Predictive design of experiments in Radiation, Electrical, and High Energy Density Science (REHEDS) requires knowledge of material properties (e.g., equations of state (EOS), transport coefficients, and radiation physics). Interpreting experimental results also requires accurate models of diagnostic observables (e.g., detailed emission, absorption, and scattering spectra). These properties and observables are all typically tabulated with dedicated models that are not mutually consistent and are restricted to Local Thermodynamic Equilibrium (LTE). This project developed a relatively fast and accurate non-LTE average-atom model based on density functional theory that provides a complete set of EOS, transport, and radiative data. That model was tested against first-principles multi-atom models and extended to non-LTE; a tabular scheme was developed that compactly captures non

LTE effects, and the tables were implemented in both the GORGON simulation code and a new post-processor—significantly advancing REHEDS modeling capabilities. The research, done in collaboration with Sandia Alliance partner University of Illinois at Urbana-Champaign, Michigan State University, Cornell University, Princeton University, and Lawrence Livermore National Laboratory, and has resulted in nine publications including 2022 articles in Scientific Reports , Journal of Physics B: Molecular and Optical Physics , and Physical Review Letters . Postdoc Alina Kononov was selected for a 2022 APS Metropolis award “For trailblazing contributions to the computational modeling of materials physics, including large-scale simulations of irradiated materials and advances in time-dependent density functional theory.” (PI: Stephanie Hansen)

A comparison of multi-center density functional theory (DFT) and DFT-molecular dynamics (DFT-MD) data and our DFT-average atom (DFT-AA) model for iron at ρ = 7.9 g/cc and T = 1 eV: (a) valence-shell electronic densities of state, (b) radial electron densities with error bars representing averages over ions for DFT MD and two plausible definitions of ionized electrons in DFT-AA, and (c) radial ion distributions for the two definitions of ionization.

Steady-state K-shell group radiation energy density for a uniform plasma cylinder of aluminum with ni = 1020 ions/cc and Te = 500 eV [7] using 12, 24, and 48 rays for radiation transport, (b) lineouts of radiation energy density from the 12-angle case aligned (red) and between (black) rays, and from the 48-angle cases between rays (blue); black dashed lines denote the edges of the plasma cylinder.

83

LABORATORY DIRECTED RESEARCH & DEVELOPMENT