Magnetic ordering and electron correlation of iron-based superconductor (Ca3Al2O5−x)(Fe2As2) from first-principles study

In this paper the density-functional theory calculations are performed on the newly discovered superconductor (Ca3Al2O5−x)(Fe2As2). Within the LSDA approach, the total-energy calculations show that the ground state is in striped anti-ferromagnetic (S-AFM) order for (Ca3Al2O5−x)(Fe2As2) (x=0 and 0.5) and oxygen vacancy is easily formed at 8g site for (Ca3Al2O5−x)(Fe2As2) (x=0.5). The electronic densities of the states around the Fermi energy (EF) mainly come from the Fe-3d states for both nonmagnetic and S-AFM configurations of (Ca3Al2O5−x)(Fe2As2) (x=0) and the total DOSs (both spins) around the EF become obviously larger when oxygen vacancies are introduced at 8g site. Considering electron correlation, it is found that a strong correlation insulating gap develops with the increase of Hubbard U for the parent compound (Ca3Al2O5)(Fe2As2), and the transition from insulator to metal is forecasted when oxygen vacancies are introduced in (Ca3Al2O5−x)(Fe2As2) system. The ground state of this compound could be ascribed as a correlated insulator and the oxygen vacancy yields its transition from insulator to metal.