ABSTRACT
In the present chapter, we mainly focus on theoretical studies which
adopt material specific model Hamiltonians that take into account
the band structure obtained from first principles calculation. In
particular, we pay special attention to the studies based on the
models that consider all five of the Fe 3d bands. We first review the model construction from the first principles band calculation, and
then describe the main features of the band structure and the Fermi
surfaces. We then discuss how the many body interactions together
with these peculiar band structures and Fermi surfaces result in
the development of spin fluctuations or antiferromagnetism. As for
the mechanism of superconductivity, we describe mainly the spin-
fluctuation-mediated pairing, while we also comment on some other
possibilities. Finally, we give a review on how the electronic states
depend on the materials, affecting both the spin fluctuations and the
superconductivity.
