Ionization Potential Depression in Dense Plasmas Predicted with <i>Ab Initio</i> Methods

The degree of ionization is an important quantity that directly affects the equation of state of plasmas as well as their optical and transport properties. At high density, the electronic states are affected by the interaction with nearby particles. In energy space, bound states are pushed closer to the continuous spectrum of free-particle states. These changes are typically encapsulated in the terms of ionization potential depression (IPD). An accurate description of IPD becomes important when spectroscopic measurements are employed to determine the thermodynamic state of plasmas. In their seminal work, Stewart and Pyatt (SP) have developed an analytical model to describe the IPD. However, in Physical Review E 97 (2018) 063207, diverging trends between SP predictions and ab initio results were reported for hot, dense aluminum. Here, we report results from a comprehensive set of density functional molecular dynamics simulations that were designed to study the IPD of different materials under various thermodynamic conditions. We analyze the strengths and weaknesses of SP models and discuss possible reasons why they may become unreliable at high density.