  The symmetry of the order parameter in iron-based superconductors, especially
the presence or absence of nodes, is still a question of debate. While
contradictory experiments can be explained by appropriately tuned theories of
nodeless superconductivity in the iron-arsenide compounds, for LaOFeP all
experiments clearly point to a nodal order parameter. We put forward a scenario
that naturally explains the difference between the order-parameter character in
these two sets of compounds, and use functional renormalization group (fRG)
techniques to analyze it in detail. Our results show that, due to the orbital
content of the electron and hole bands, nodal superconductivity on the electron
pockets (hole pocket gaps are always nodeless) can naturally appear when the
third hole pocket which lies at wavevector (pi,pi) in the unfolded Brillouin
zone is absent, as is the case in LaOFeP. When present, the third hole pocket
has overwhelming d_{xy} orbital character, and the intra-orbital interaction
with the d_{xy} dominated part of the electron Fermi surface is enough to drive
the superconductivity nodeless (of s^+- form). However, in its absence, pair
hopping, inter-orbital, and electron-electron intra-orbital interactions render
the gap on the electron pockets softly nodal.
