Ab initio phonon dispersions of Fe and Ni

We present the ab initio phonon dispersions of magnetic bcc Fe and fee Ni. Our calculations are carried out in the framework of density functional per turbation theory (DFPT), using ultrasoft pseudopotentials, spin-polarized g eneralized gradient approximations, and nonlinear core; corrections. The im plementation of the above techniques within DFPT is discussed. We find that these approximations, together, provide phonon dispersions which are in go od agreement with experiment, while the local spin density approximation sy stematically overestimates the experimental frequencies.