Density-functional average-atom model for first-principles simulations of warm dense matter

The warm dense matter regime is notoriously challenging from a computational modelling perspective, since a quantum mechanical description is required for large length and time scales, at temperatures well above the ground-state. Average-atom (AA) models reduce the many-body system of interacting electrons and nuclei to an effective ‘average’ atom, with relevant properties typically computed via Kohn–Sham density-functional theory (KS-DFT): this approach has clear computational advantages relative to full ab initio KS-DFT (or alternative) simulations. However, there is some uncertainty regarding the accuracy and predictive capabilities of AA models. In this talk, I will present a first principles derivation of a KS-AA model, carefully analysing the assumptions made and terms neglected in this approach. The results obtained from our model highlight the importance of the choice of boundary conditions and the significance of the self-interaction error. I will discuss the implications of these findings for future developments in AA models.