Fe2: As simple as a Herculean labour. Neutral (Fe2), cationic (Fe2(+)), and anionic (Fe2(-)) species

We have studied 175 molecular states of the Fe2 diatomic by constructing full potential energy curves dissociating to the ground Fe((5)D) + Fe((5)D) and first excited Fe((5)D) + Fe((5)F) dissociation channels by multireference configuration interaction methods and large basis sets. The ground X(9)Σg (-) and the first excited (7)Σu (-) states have been detailed by a multitude of plain and explicitly correlated F12 methods at both the valence and core-valence computational levels. The potential curves of most of the states present strong interactions/avoided crossings that trigger a severe non adiabatic behavior. For reasons of completeness, the ground states of the charged Fe2 (-,+) species have also been considered.