  The results of neutron scattering and angle-resolved photoemission
experiments for the Fe-pnictide parent compounds, and their metallic nature,
are shown to impose severe constraints on the range of values that can be
considered "realistic" for the intraorbital Hubbard repulsion U and Hund
coupling J in multiorbital Hubbard models treated in the mean-field
approximation. Phase diagrams for three- and five-orbital models are here
provided, and the physically realistic regime of couplings is highlighted, to
guide future theoretical work into the proper region of parameters of Hubbard
models. In addition, using the random phase approximation, the pairing
tendencies in these realistic coupling regions are investigated. It is shown
that the dominant spin-singlet pairing channels in these coupling regimes
correspond to nodal superconductivity, with strong competition between several
states that belong to different irreducible representations. This is compatible
with experimental bulk measurements that have reported the existence of nodes
in several Fe-pnictide compounds.
