Weak Coulomb correlations stabilize the electride high-pressure phase of elemental calcium.

Theoretical studies using the state-of-the-art DFT+DMFT method show that weak electronic correlation effects are crucial for reproducing the experimentally observed phase transitions fromβ-tin toCmmmand then to the simple cubic structure under high pressure. The formation of an electride in calcium leads to the emergence of partially filled and localized electronic states under compression. The electride state was described using a basis containing molecular orbitals centered on the interstitial site and Ca-d states. We investigate the influence of Coulomb correlations on the structural properties of elemental Ca, noting that approaches based on the Hartree-Fock method (DFT+U or hybrid functional schemes) are poorly suited for describing correlated metals. We find that only the DFT+DMFT method reproduces the correct sequence of high-pressure phase transitions of Ca.