Center for Advanced Systems Understanding (CASUS), Gorlitz (Germany); Helmholtz-Zentrum Dresden-Rossendorf (HZDR) (Germany); Univ. of Rostock (Germany)
Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)
Univ. zu Kiel (Germany)
SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States)
Center for Advanced Systems Understanding (CASUS), Gorlitz (Germany); Helmholtz-Zentrum Dresden-Rossendorf (HZDR) (Germany)
Helmholtz-Zentrum Dresden-Rossendorf (HZDR) (Germany); Univ. of Rostock (Germany)
Center for Advanced Systems Understanding; Helmholtz-Zentrum Dresden-Rossendorf (HZDR) (Germany)
Warm dense matter (WDM) is an active field of research, with applications ranging from astrophysics to inertial confinement fusion. Ionization degree and continuum lowering are important quantities to understand how materials behave under these conditions, but can be difficult to diagnose since experimental campaigns are limited and often require model-dependent analysis. This is especially true for hydrogen, which has a comparably low scattering cross section, making high-quality data particularly difficult to obtain. Consequently, building equation of state tables often relies on simulations in combination with untested approximations to extract properties from experiments. Here, we investigate an approach for extracting the ionization potential depression and ionization degree—quantities which are otherwise not directly accessible from the physical model—from first-principles path integral Monte Carlo (PIMC) simulations utilizing a chemical model. In contrast to experimental measurements, where noise and nonequilibrium effects add to the uncertainty of the inferred parameters, PIMC simulations provide a clean signal with well-defined thermodynamic conditions. Comparisons against commonly used models show a qualitative agreement, but we find deviations primarily for the high-density and high-temperature cases. We also demonstrate the decreasing sensitivity of the dynamic structure factor with respect to both ionization and continuum lowering for increasing scattering angles in x-ray Thomson scattering experiments. Our work has important implications for the design of future experiments, but also offers qualitative understanding of structure factors and the imaginary-time correlation function obtained from first-principles quantum Monte Carlo simulations.
Bellenbaum, Hannah M., et al. "Estimating ionization states and continuum lowering from <em>ab initio</em> path integral Monte Carlo simulations for warm dense hydrogen." Physical Review Research, vol. 7, no. 3, Jul. 2025. https://doi.org/10.1103/9d7r-1xbm
Bellenbaum, Hannah M., Böhme, Maximilian P., Bonitz, Michael, Döppner, Tilo, Fletcher, Luke B., Gawne, Thomas, Kraus, Dominik, Moldabekov, Zhandos A., Schwalbe, Sebastian, Vorberger, Jan, & Dornheim, Tobias (2025). Estimating ionization states and continuum lowering from <em>ab initio</em> path integral Monte Carlo simulations for warm dense hydrogen. Physical Review Research, 7(3). https://doi.org/10.1103/9d7r-1xbm
Bellenbaum, Hannah M., Böhme, Maximilian P., Bonitz, Michael, et al., "Estimating ionization states and continuum lowering from <em>ab initio</em> path integral Monte Carlo simulations for warm dense hydrogen," Physical Review Research 7, no. 3 (2025), https://doi.org/10.1103/9d7r-1xbm
@article{osti_2575656,
author = {Bellenbaum, Hannah M. and Böhme, Maximilian P. and Bonitz, Michael and Döppner, Tilo and Fletcher, Luke B. and Gawne, Thomas and Kraus, Dominik and Moldabekov, Zhandos A. and Schwalbe, Sebastian and Vorberger, Jan and others},
title = {Estimating ionization states and continuum lowering from <em>ab initio</em> path integral Monte Carlo simulations for warm dense hydrogen},
annote = {Warm dense matter (WDM) is an active field of research, with applications ranging from astrophysics to inertial confinement fusion. Ionization degree and continuum lowering are important quantities to understand how materials behave under these conditions, but can be difficult to diagnose since experimental campaigns are limited and often require model-dependent analysis. This is especially true for hydrogen, which has a comparably low scattering cross section, making high-quality data particularly difficult to obtain. Consequently, building equation of state tables often relies on simulations in combination with untested approximations to extract properties from experiments. Here, we investigate an approach for extracting the ionization potential depression and ionization degree—quantities which are otherwise not directly accessible from the physical model—from first-principles path integral Monte Carlo (PIMC) simulations utilizing a chemical model. In contrast to experimental measurements, where noise and nonequilibrium effects add to the uncertainty of the inferred parameters, PIMC simulations provide a clean signal with well-defined thermodynamic conditions. Comparisons against commonly used models show a qualitative agreement, but we find deviations primarily for the high-density and high-temperature cases. We also demonstrate the decreasing sensitivity of the dynamic structure factor with respect to both ionization and continuum lowering for increasing scattering angles in x-ray Thomson scattering experiments. Our work has important implications for the design of future experiments, but also offers qualitative understanding of structure factors and the imaginary-time correlation function obtained from first-principles quantum Monte Carlo simulations.},
doi = {10.1103/9d7r-1xbm},
url = {https://www.osti.gov/biblio/2575656},
journal = {Physical Review Research},
issn = {ISSN 2643-1564},
number = {3},
volume = {7},
place = {United States},
publisher = {American Physical Society (APS)},
year = {2025},
month = {07}}
Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)
Sponsoring Organization:
European Research Council (ERC); USDOE Laboratory Directed Research and Development (LDRD) Program; USDOE National Nuclear Security Administration (NNSA); USDOE Office of Science (SC), Fusion Energy Sciences (FES)
Dornheim, Tobias; Vorberger, Jan; Moldabekov, Zhandos A.
Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, Vol. 381, Issue 2253https://doi.org/10.1098/rsta.2022.0217