Reconciling Ionization Energies and Band Gaps of Warm Dense Matter Derived with Ab Initio Simulations and Average Atom Models

Average atom (AA) models allow one to efficiently compute electronic and optical properties of materials over a wide range of conditions and are often employed to interpret experimental data. However, at high pressure, predictions from AA models have been shown to disagree with results from ab initio computer simulations. We represent a new AA model, AvIon, that computes the electronic eigenstates with novel boundary conditions within the ion sphere. Bound and free states are derived consistently. We drop the common AA assumption that the free-particle spectrum starts at the potential threshold, which we found to be incompatible with ab initio calculations. We perform ab initio simulations of crystalline and liquid states for several elements over a wide range of densities and show that the computed band structures are in excellent agreement with predictions from AvIon.