A Study of the Electronic and Ionic Structure, for Competing States of Fully and Partially Ionized Hydrogen, Using the Neutral Pseudo‐Atom Method as Well as a Classical Map for the Electron Subsystem

ABSTRACT Prof. Bonitz and his collaborators have made seminal contributions to the study of the uniform electron fluid and the electron‐proton fluid, viz., hydrogen, in using ab initio simulations. as reflected in this festschrift. Here we review the theoretical methods available for these systems where traditional small‐parameter methods fail. We use the neutral‐pseudo atom (NPA) method, and a classical map for quantum electrons to study hydrogen plasmas. We show that both fully‐ionized and partially‐ionized hydrogen phases can exist with the same nominal density and temperature, at pressures and temperatures of interest to planetary physics. The mean ionization , pair‐distribution functions, free energies, pressures and conductivities are calculated for the competing phases. Here is also a measure of the miscibility of fully ionized and un‐ionized hydrogen. Recent studies using path‐integral Monte Carlo methods, and ‐atom Density Functional Theory (DFT) simulations have provided essential structure data including the electron–electron structure factor that enters into interpretation of x‐ray Thomson scattering and other diagnostics. We show that these structure data can be inexpensively evaluated using classical‐map schemes for fully ionized plasmas, and more generally, using one‐atom (average‐atom) DFT methods for partially ionized systems.