First-principles calculations based on the generalized gradient corrected d
ensity-functional theory reveal that iron tetraoxide (FeO4), in spite of it
s closed-shell structure, has an electron affinity that is larger than that
of any known halogen atom. This novel property is shown to be a manifestat
ion of the special bonding characteristics of d-electron systems and can pl
ay an important role in chemical and biological processes. [S1050-2947(99)0
1505-X].