  The coupling of Fe magnetic moments in LaFeAsO$_{1-x}$F$_{x}$ with the As
$A_{1g}$ phonon is calculated. We present first principles calculations of the
atomic and electronic structure of LaFeAsO as a function of electron doping. We
perform calculations using the virtual crystal approximation as well as
supercell calculations with F substitutional impurity atoms. The results
validate the virtual crystal approximation for the electronic structure near
the Fermi level. Its is found that 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 $\lambda$ is obtained
if the coupling between the $A_{1g}$ 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. The implications of these results on the superconducting
transition are discussed

Superconductivity