Embedding Theory Approach to Average Atom Models for Warm Dense Matter*

Density Functional Theory (DFT)-based Average Atom Models (AAM) provide useful physical insight for the Warm Dense Matter (WDM) regime by reducing the ionic many-body system to a spherical average over local environments or charge states. However, AAMs tend to fall short of providing an accurate picture of electron-electron and electron-ion interactions. Typical approaches account for interactions by imposing boundary conditions; other schemes use closure relations from plasma physics to model ion-ion correlations (two-component plasma TCP-AAM). We propose a DFT embedding theory approach to handle interactions in the AAM in which we consider the average atom embedded in a background plasma described by an ion pair correlation function, e.g. as calculated from TCP-AAM and full quantum mechanical treatments such as quantum molecular dynamics (QMD). The connection between the embedded atom and background plasma subsystems is made by the nonadditive kinetic potential V^NAD which can be calculated from Thomas-Fermi and von Weizsäcker or more advanced kinetic energy functionals. We apply this approach to modelling a dense hydrogen plasma. Thermodynamic properties generated from this scheme can provide a benchmark comparison against existing AAMs and QMD to validate our approach.