  We present first principles calculations of the atomic and electronic
structure of electron-doped LaOFeAs. We find that whereas the undoped compound
has an antiferromagnetic arrangement of magnetic moments at the Fe atoms, the
doped system becomes non magnetic at a critical electron concentration. We have
studied the electron-phonon interaction in the doped paramagnetic phase. For
the $A_{1g}$ phonon, the separation between the As and Fe planes induces a
non-collinear arrangement of the Fe magnetic moments. This arrangement is anti
parallel for interactions mediated by As, and perpendicular for Fe-Fe direct
interactions, thus avoiding frustration. This coupling of magnetism with
vibrations induces anharmonicities and an electron-phonon interaction much
larger than in the pure paramagnetic case. We propose that such enhanced
interactions play an essential role in superconducting compounds close to an
atiferromagnetic phase transition.
