First-principles derivation and properties of density-functional average-atom models

Finite-temperature Kohn-Sham density functional theory (KS-DFT) is a widely-used method in warm dense matter (WDM) simulations and diagnostics. Unfortunately, full KS-DFT-molecular dynamics models scale unfavourably with temperature there remains uncertainty regarding the performance of existing approximate exchange-correlation (XC) functionals under WDM conditions. Of particular concern expected explicit dependence XC on temperature, which absent from most approximations. Average-atom (AA) models, significantly reduce computational cost KS-DFT calculations, have therefore become an integral part modeling. In this paper, we present derivation first-principles AA model fully-interacting many-body Hamiltonian, carefully analyzing assumptions made terms neglected reduction. We explore impact different choices within model---such as boundary conditions functionals---on common properties WDM, for example equation-of-state data, ionization degree behavior frontier energy levels. Furthermore, drawing upon insights ground-state KS-DFT, discuss likely sources error KS-AA possible strategies mitigating such errors.