  Using the fluctuation-exchange (FLEX) approximation we study an effective
five-band Hubbard model for iron-pnictide superconductors obtained from the
first-principles band structure. We preclude deformations of the Fermi surface
due to electronic correlations by introducing a static potential, which mimics
the effect of charge relaxation. Evaluating the Eliashberg equation for various
dopings and interaction parameters, we find that superconductivity can sustain
higher hole than electron doping. Analyzing the symmetry of the superconducting
order parameter we observe clear differences between the hole and electron
doped systems. We discuss the importance of the pnictogen height for
superconductivity. Finally, we dissect the pairing interaction into various
contributions, which allows us to clarify the relationship between the
superconducting transition temperature and the proximity to the
anti-ferromagnetic phase.
