Effects of Fluorine Doping and Pressure on the Electronic Structure of LaO1-xFx FeAs Superconductor: a First Principle Study

The effects of fluorine doping on the electronic structure of LaO1-xFxFeAs superconductor have been investigated by ab initio density functional theory using pseudopotential quantum espresso code. Firstly, we have studied the role of fluorine doping on the electronic structure of LaO1-xFxFeAs by calculation of band structure, density of states, and Fermi surfaces at various doping levels x = 0.00, 0.25, and 0.50. The lattice parameters and ionic position have been determined by optimizing crystal structure. Our results show that doping decreases cell volume similar to mechanical pressure and shifts the bands and states near the Fermi level toward the lower energies. According to the Fermi surface calculations, compound with x = 0 has the long-range spin density wave (SDW) like magnetic order but compounds with x = 0.25 and x = 0.50 have no magnetic orders. Therefore, fluorine doping can help creating the superconducting state in these compounds by suppressing their magnetic orders. Finally, in order to study the supplementary effects of fluorine doping and pressure, we have calculated the density of states and band structure of the compound with doping level x = 0.50 under different pressures. The results show there is a certain pressure in which density of states near the Fermi level is maximum.