Accurate and efficient calculations of mean ionization states with an average-atom model

The mean ionization state (MIS) is a critical property in dense plasma and warm dense matter research. It is used (for example) as an input parameter in various models, including for example the calculation of adiabats in inertial confinement fusion; it is also used to help interpret and fit experimental results. Unfortunately however, theoretical predictions of the MIS are often inconsistent with each other and experimental data. In this presentation, I will compute the MIS using a variety of approaches in an average-atom model and compare results with higher-fidelity simulations and experimental benchmarks [1]. I will show that the canonical approach for computing the MIS is usually insufficient; I will also discuss a novel approach based on the electron localization function, which yields improved results but tends to systematically under-estimate the MIS. Finally, I will adapt a recently-proposed Kubo–Greenwood method [2] to our computationally efficient average-atom model, which shows very promising agreement with all the benchmarks considered, with one example shown in Fig. 1 below.

[1] Callow, Kraisler and Cangi, arXiv:2203.05863 (2022)
[2] Bethkenhagen et al., Phys. Rev. Research 2, 023260 (2020)