  Using first-principle density functional theory calculations combined with
insight from a tight-binding representation, dynamical mean field theory, and
linear response theory, we have extensively investigated the electronic
structures and magnetic interactions of nine ferropnictides representing three
different structural classes. The calculated magnetic interactions are found to
be short-range, and the nearest ($J_{1a}$) and next-nearest ($J_{2}$) exchange
constants follow the universal trend of J_{1a}/2J_{2}\sim 1, despite their
itinerant origin and extreme sensitivity to the z-position of As. These results
bear on the discussion of itineracy versus magnetic frustration as the key
factor in stabilizing the superconducting ground state. The calculated spin
wave dispersions show strong magnetic anisotropy in the Fe plane, in contrast
to cuprates.
