  The momentum distribution function (MDF) bands of iron-group transition
metals from Sc to Cu have been investigated on the basis of the
first-principles momentum dependent local ansatz wavefunction method. It is
found that the MDF for $d$ electrons show a strong momentum dependence and a
large deviation from the Fermi-Dirac distribution function along high-symmetry
lines of the first Brillouin zone, while the $sp$ electrons behave as
independent electrons. In particular, the deviation in bcc Fe (fcc Ni) is shown
to be enhanced by the narrow $e_{g}$ ($t_{2g}$) bands with flat dispersion in
the vicinity of the Fermi level. Mass enhancement factors (MEF) calculated from
the jump on the Fermi surface are also shown to be momentum dependent. Large
mass enhancements of Mn and Fe are found to be caused by spin fluctuations due
to $d$ electrons, while that for Ni is mainly caused by charge fluctuations.
Calculated MEF are consistent with electronic specific heat data as well as the
recent angle resolved photoemission spectroscopy data.
