Matter at Extreme Conditions: I

Recent advances in electronic structure calculations have provided deeper insights into electronic and magnetic phase transitions in solids under extreme compression. Building on our earlier investigations of diamond-structure silicon, this work focuses on compressed hcp cobalt by employing density functional theory (DFT) with semilocal and hybrid functionals as well as DFT+U, using fine k-grids to converge the magnetization. Specifically, we investigated the critical compression at which cobalt undergoes an electronic phase transition from metal to semimetal and insulator (for fixed hcp crystal structure), and examined how this transition correlates with the vanishing of magnetism and formation of an electride. Additionally, we looked at the phase diagram of pressure and electronic temperature to explore the combined effects on the magnetic properties, identifying regions where magnetism is present and where it disappears. This work provides understanding of how extreme pressure and temperature impact the electronic structure and magnetism of hcp cobalt, and assesses the accuracy of different theoretical approaches.