Coupling of magnetic moments with phonons and electron-phonon interaction in LaFeAsO1-xFx

The coupling of Fe magnetic moments in LaFeAsO1−xFx with the As A1g phonon is calculated. We present first-principles calculations of the atomic and electronic structure of LaFeAsO1−xFx as a function of electron doping. We perform calculations using the virtual crystal approximation as well as supercells with F substitutional impurity atoms. The results validate the virtual crystal approximation for the electronic structure near the Fermi level. The electronic density of states at the Fermi level is maximum for x = 0.125, enhancing the electron-phonon interaction. An additional increase of the electron-phonon parameter λ is obtained if the coupling between the A1g phonon and the Fe magnetic moment is included. It is found that the electron-phonon interaction can be one order of magnitude larger than its value if no spin resolution is included in the calculation.