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We report the results of the second charged-particle transport coefficient code comparison workshop, which was held in Livermore, California on 24–27 July 2023. This workshop gathered theoretical, computational, and experimental scientists to assess the state of computational and experimental techniques for understanding charged-particle transport coefficients relevant to high-energy-density plasma science. Data for electronic and ionic transport coefficients, namely, the direct current electrical conductivity, electron thermal conductivity, ion shear viscosity, and ion thermal conductivity were computed and compared for multiple plasma conditions. Additional comparisons were carried out for electron–ion properties such as the electron–ion equilibration time and alpha particle stopping power. Overall, 39 participants submitted calculated results from 18 independent approaches, spanning methods from parameterized semi-empirical models to time-dependent density functional theory. In the cases studied here, we find significant differences—several orders of magnitude—between approaches, particularly at lower temperatures, and smaller differences—roughly a factor of five—among first-principles models. We investigate the origins of these differences through comparisons of underlying predictions of ionic and electronic structure. The results of this workshop help to identify plasma conditions where computationally inexpensive approaches are accurate, where computationally expensive models are required, and where experimental measurements will have high impact.
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Comparison of transport models in dense plasmas
We compare a variety of models used for the calculation of transport coefficients in dense plasmas, including average-atom models, models based on kinetic theory, structure matching effective potentials, and pair-potential molecular dynamics. In particular, we focus on the parameter space investigated in the second charged-particle transport coefficient code comparison workshop [Stanek et al., Phys. Plasmas 31, 052104 (2024)]. Each model is based on the self-consistent output of our average-atom calculations. Ionic transport properties are generated from implicit electron pair matched molecular dynamics simulations, bypassing the need for either dynamical electron simulations or on-the-fly electronic structure calculations. These matched pair potentials are generated in a nonlinear way using a classical mapping procedure, further avoiding an expensive force-matching procedure. We compare these results with the density functional theory data presented at the workshop, as well as a set of widely used parametric models, which we have modified to enhance accuracy, especially at the low- and high-temperature extremes of the parameter space. We also detail the non-trivial statistical aspect of converging ionic transport coefficients.
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- Award ID(s):
- 2108505
- PAR ID:
- 10591863
- Publisher / Repository:
- American Institute of Physics
- Date Published:
- Journal Name:
- Physics of Plasmas
- Volume:
- 31
- Issue:
- 8
- ISSN:
- 1070-664X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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