Electron localization and phase transitions in solids under extreme compression*

Under high energy density conditions, solids can undergo electronic and magnetic phase changes, and these can happen even if the crystal structure is retained the same. Our recent findings using density functional theory (DFT) showed re-entrant semimetallicity in diamond structure silicon, and a metal à insulator transition in hcp cobalt, due to electride-like behavior. To improve on these DFT-PBE calculations, we use some advanced beyond-DFT (GW/BSE) approximation, to identify more accurately the critical pressures for phase transitions of silicon and cobalt. We study the charge density, density of states, electronic bandstructure, dielectric function, and magnetization of compressed silicon and cobalt. Furthermore, we assess the applicability of plasma-based ionization models for solid silicon. This investigation gives better insight into the generality of electronic and magnetic phase changes in solids under high energy density conditions, and the degree to which they can be predicted by a common ionization model.